What equal annual series of payments must be paid into a sinking fund to accumulate the following

Question:

What equal annual series of payments must be paid into a sinking fund to accumulate the following amounts?
(a) $32,000 in 15 years at 8% compounded annually
(b) $55,000 in 10 years at 6% compounded annually
(c) $35,000 in 20 years at 7% compounded annually
(d) $8,000 in 4 years at 11% compounded annually