JB Enterprises has a cost of capital of $12\%.$ Calculate the present value of the following investment opportunities:

Note: Round answers to two decimal places.

a$.$ An investment project promises a return of $$4,200$ at the end of year $3$ an$.$ $$7,0$ at the end year $4.$

b$.$ An investment project promises a return of $$2,800$ at the end of each of the next four years.