What amount must you invest now in order to have $15,000 in 12 years if you can get 8% annual interest?

[2] About what interest rate would you need to get if you invested $10,000 now and needed to have $15,000 in 7 years?

[2] About how long would you have to wait for $8,000 to accumulate to $20,000 if you could get 12% interest? [2]