You wish to retire after 30 years, at which time you want to have accumulated enough money to receive an annual income of $55,000 at year end. During the period before retirement, you can earn 9 percent annually, while after retirement you can earn 7 percent on your money. You plan to deposit 4,000 at the end of each year for 30 years till you retire. How many years will your retirement fund last?

a 17.5

b 15.0

c 12.0

d 20.0