Total Present Value of Income Flows

A company is considering a major investment programme, with a choice of two projects A and B.

Project A : Initial outlay $7800 but then promises income streams of

Year 1: Income Stream $11500

Year 2: Income Stream $8200

Year 3: Income Stream $5000

Year 4: Income Stream $2400

Project B : Initial Outlay $6600 with income streams of

Year 1: Income Stream $10300

Year 2: Income Stream $8000

Year 3: Income Stream $4000

Year 4: Income Stream $850

The current rate of interest is 4.5 %

I have to calculate the total present value of the income flow from project A and project B, over the four year period.

Could anyone just point me in the right direction as to what I’m supposed to do here? In other examples I’ve looked at there always seems to be a discount rate (is that the same as the interest rate?)