Write the quadratic function f(x) = x2 + 8x + 3 in vertex form.
a) f(x) = (x - 4)2 - 13
b) f(x) = (x - 4)2 + 3
c) f(x) = (x + 4)2 + 3
d) f(x) = (x + 4)2 - 13

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?