Calculate the following values, assuming a discount rate of 8%:

a. present value of a perpetuity (also called a perpetual annuity) of $50 received each year at the end of each year

b. present value of an annuity of $50 received at the end of each year for 5 years

c. present value of an annuity of $50 received at the end of each year for 10 years, with the first payment to be received at the end of the 6^th year

d. present value of a perpetuity of $50, with the first payment received at the end of the 16^th year