Since you got a 1099-B, the simplest thing is to report it as taxable income. You did sell stocks (or rather the state sold them for you).
You would indicate that you inherited them, and the cost basis is 6 shares x the share price on the date your mother died. You can look this up on the Comcast web site. (It's about $13-$14 each.) Selling date is the date you got the check from the state unclaimed property department. You'll have a capital gain of around $215.
