The difference between a number and 12 is 20

Solve this problem! extra ! 3025/5.5 = a/90.75

Sam opened a money-market account that pays 3% simple interest. he started the account with $7,000 and made no further deposits. when he closed the account, he had earned $420 in interest. how long did he keep his account open?

Y+ 2/y is it a polynomial in one variable or not? and if so, why?