$1.$ Equal Payment Series. What equal annual payment series is required to repay the following amounts?

a$.$ $$3$ million in $50$ years at $6\%$ interest, compounded annually

b$.$ $$12,000$ in $15$ years at $6\mathrm{.}25\%$ interest, compounded annually

c$.$ $$2,500$ in $5$ years at $7\mathrm{.}5\%$ interest, compounded annually

d$.$ $$7,500$ in $7$ years at $5\mathrm{.}25\%$ interest, compounded annually