What equal series of payments must be paid into a sinking fund in order to accumulate each given amount? (a) $12,000 in 8 years at 8% compounded semiannually when payments are semiannual. (b) $2,000 in 16 years at 7% compounded quarterly when payments are quarterly. (c) $38,000 in four years at 7.45% compounded monthly when payments are monthly.