The graph of y=|x|y=∣x∣y, equals, vertical bar, x, vertical bar is scaled vertically by a factor of \dfrac{7}{2} 2 7 start fraction, 7, divided by, 2, end fraction.

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?