Present Values. Compute the present value of a $$100$ cash flow for the following combinations of discount rates and times. Include the formula used to make the calculations. Note: See page $50$ and $51$ of the online resource; the general formula is:

Present Value $=$ Future Value after t periods $/(1+$ r$)$t

a$.$ r $=12\%$; t $=10$ years

b$.$ r $=12\%$; t $=20$ years

c$.$ r $=7$ percent; t $=10$ years

d$.$ r $=7$ percent; t $=20$ years