Find the present value of the following ordinary annuities:
a. $400 per year for 10 years at 10%
b. $200 per year for 5 years at 5%
c. $400 per year for 5 years at 0%
d. Now rework, parts a, b, and c assuming that payments are made at the beginning of each year; that is, they are annuities due.