Why are we more likely to need to calculate the PV of cash flow streams than the FV of streams? What is the future value of this cash flow stream: $100 at the end of one year, $150 due after two years, and $300 due after three years if the appropriate interest rate is 15 percent?

Finance by Geoffrey

Why are we more likely to need to calculate the PV of cash flow
streams than the FV of streams?
What is the future value of this cash flow stream: $100 at the end of
one year, $150 due after two years, and $300 due after three years if
the appropriate interest rate is 15 percent?