Question: I'm 63 years old and retired last fall. I would like to work part-time to make a few extra dollars, but I understand this might affect my Social Security. True ?

Answer: True. A person in your age group --that is, under 65 -- may earn up to $3,720 in 1980 without losing Social Security benefits.

But if your earned income goes over that amount, you will have to give up $1 in Social Security money for every $2 over the ceiling.

Those who have reached age 65 are subject to a similar rule, but the ceiling on earned income for that grouup is $5,000.

And for those age 72 older there is no limit; Social Security payments for people in that age group are not reduced regardless of the amount of income earned during the year.

Incidentally, only income earned by working is counted. Your Social Security benefit is not affected by income from company retirement plans, IRA or Keogh programs, investment interest or dividends, or from rental property.

(Caution: Income from rental property or from a business could be considered "earned" if you devote a substantial amount of time to its management.)

Q: I want to sell some stock to my sister-in-law without going through a broker and paying the fee. Is this possible? If so, how is it done ?

A: Yes, it's possible -- by sending the stock certificate to the transfer agent (shown on the certificate) along with a letter asking that the certificate be reissued to your sister-in-law.

You (and any co-owners) must sign theback of the certificate -- or a separte "stock power" --exactly as the name(s) appears on the front. Your accompanying letter of instructions must also be signed the same way.

The signature on each document must be authenticated by an official of a commercial bank or trust company or a stock brokerage house. And the letter must give the name, address, and Social Security number of the new owner.

There may be a small transfer fee, and you may be liable for transfer tax as well. You might write to the transfer agent in advance to find out what is required in your case.

The transfer agent and the SEC are not interested in the price your sister-in-law pays you for the stock -- but the IRS is.

If you plan to report the sale for tax loss or gain purposes, and in any case to establish an acceptable cost basis for your sister-in-law, the market value of the shares on the date of sale.

The general rule is that for a sale of property to a relative to be valid for tax purposes, it must be what is called an "arm's length" transaction. That is, the terms of sale must be approximately the same as you would offer a stranger.

To document the transaction I suggest you draw up a simple bill of sale identifying the stock, the buyer and seller, the date of sale, and the price paid.

Q: I make five or six business trips a year, and often my expenses exceed the per diem I receive from my employer. Are the excess expenses deductible ?

A: The excess of expenses over reimbursement may be deductible -- but not reimbursement may be deductible -- but not on a selective basis. You can't report just those trips on which you spent more than you got, and then forget about the rest.

This means that you must keep track of all your expenses (along with substantiating receipts) for the entire year. You can then claim excess expenses only if the total for the year exceeds total reimbursements.

It probably doesn't pay to bother unless your expenses consistently exceed reimbursements, so that the total excess is substantial, or unless you keep detailed and precise records anyway.

But if your employer includes the amount of reimbursement as income on your Form W-2, then by all means you should keep the necessary records and claim your total expenses (not reduced by reimbursements, since taht amount is already accounted for). IRS Publication 463 is a handy reference.