If an investor's required rate of return is 9.6%, what is the present value of the following cash flow: $7,000 at end of year one, $11,000 at end of year two, $15,000 at the end of year three, and $22,000 at the end of year four?

a. $46,234.40

b.$49,720.00

c.$42,184.67

d.$41,111.83