8 x 10-3 is how many times as great as 4 x 10-6?
2 x 109
2 x 10-9
2 x 103
2 x 10-3

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?