Let x = a + bi and y = c + di and z = f + gi. Which statements are true? a. x + y = y + x
b. (x × y) × z = x × (y × z)
c. x – y = y – x
d. (x + y) + z = x + (y + z)
e. (x – y) – z = x – (y – z)

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?