Kindly solve manually without excel. Show detailed working. Thanks!

4. a) An annuity consisting of equal payments at the end of every quarter for four years is purchased today for $ 20,000. If the interest rate is 5% compounded quarterly, how much is each payment ? b) A debt of $ 1000 due in four years and $ 1500 due in six years is to be repaid by a single payment two years from now. If the interest rate is 7 % compounded annually how much is the single payment ? [5+5=10]