Hi, is a & b correct? please help because I got stuck on c & d. Thanks

Today is January 1, year 1. Assuming an 8% discount rate, what is the future value of each of the following cash flows?

a. Future value in 3 years of $50 received now, i.e., the value on December 31, year 3

FV = PV x (1+i)ⁿ, FV = 50 x (1.08)³ = 62.99

b. Future value in 100 years of $50 received now, i.e., the value on December 31, year 100

FV = PV x (1+i)ⁿ, FV = 50 x (1.08)¹⁰⁰ = 109,988.06

c. Future value at the end of 20 years of $50 received each year at the end of the year, i.e., the value at December 31, year 20, with one payment received each December 31 from year 1 to year 20

d. Future value at the end of 20 years of $50 received each year at the beginning of the year, i.e., the value at December 31, year 20, with one payment received each January 1 from year 1 to year 20.