Compute the present value of a $$250$ cash flow for the following combinations of discount rates and times.

Note: Do not round intermediate calculations. Round your answers to $2$ decimal places.

a$.r=8\%$;$t=10$ years

b$.r=8\%$;$t=20$ years

c$.r=4\%$;$t=10$ years

d$.r=4\%$;$t=20$ years

a$.$ Present value

b$.$ Present value

c$.$ Present value

d$.$ Present value