Calculate the present value of the following payments: 

a) $600 two years from now when the interest rate is 5% 

b) $600 two years from now when the interest rate is 10% 

c) $600 4 years from now when the interest rate is 10% 

d) what do these calculations indicate about the present value of payments further in the future? 

e) what do these calculations indicate about the present value as the interest rate rises