Aladder is sliding down a wall so that the distance between the top of the ladder and the floor is decreasing at a rate of 9 feet per second. how fast is the base of the ladder receding from the wall?

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?