Help pleaseee

you need to find x

At the beginning of 1974/75,2 years a man invested #2000 in a bank at 12.5% compound interest, if it degree #650 at the end of each two years to pay his son's school fees, after payment of interest to pay his son's school fees, how much did he have left at the beginning of the 1978/79 school year?

If the tip varies directly with the number of guest which equation represents between the tip,t, and the number of guest,g?

Find the value of x. also give me an explanation so i can complete it to other questions as well, : )