The water level in a rectangular swimming pool measuring 60 feet by 20 feet is to be lowered by 6 inches. How many gallons of water must be removed? (1 cu ft = 7.5 gallons)
Pick:  A) 100  B) 250  C) 4500  D) 1200  E) 5625

Rationale: "6 inches = 1 / 2 feet ( there are 12 inches in a foot . ) , so 60 * 20 * 1 / 2 = 600 feet ^ 3 of water must be removed , which equals to 600 * 7.5 = 4500 gallons . answer : c ."
Answer: C