a$.)$ An investment will pay out $$1,000$ today and every two years thereafter for the next twenty years $(11$ cash flow payments$).$ Assuming that the annual rate is $4\%,$ would you take this investment if it costs $$7,100?$

b$.)$ What is the present value of the investment if it pays every three years $($instead of two years$)(11-$cash flow payments

PLEASE SOLVE IT WITH FORMULAS NOT EXCEL!