For every 1/4 of an inch a boy grows, he gains 3/4 of a pound. If the boy weighs 64 pounds when he is 52 inches tall, how many pounds will he weigh when he is 53.5 inches tall?

he grew 1.5 inches, or 6/4 inches, a total of 6 1/4 inches. 6*(3/4) = 4.5.

If he gained 4.5 pounds, then he would be 64 + 4.5 = 68.5 pounds