Compute the present value of a $100 cash flow for the following combinations of discount rates and times:

a. r=8 percent. t= 10 years

b. r=8 percent. t= 20 years

c. r=4 percent. t= 10 years

d. r=4 percent. t= 20 years

Please only attempt if you can solve the question with proper explanation. Please do not copy from Chegg.