What equal‐annual‐payment series is required in order to repay each of the following given present amounts?
(a) $18,000 in five years at 8% interest compounded annually.
(b) $4,200 in four years at 9.5% interest compounded annually.
(c) $7,700 in three years at 11% interest compounded annually.
(d) $23,000 in 20 years at 6% interest compounded annually.