Alistar has an annual income of $25,000. He decides to take classes on line and at night so that he can continue to work. After 3 years he gets his degree and immediately starts earning $32,000 per year. If it takes Alistar 6 years to recover his investment for his education, how much did it cost him?

a.

$21,000

b.

$42,000

c.

$63,000

d.

$150,000