The roof of an apartment building is rectangular and its length is 3 times longer than its width. If the area of the roof is 768 feet squared, what is the difference between the length and the width of the roof?
Choices
A) 32 .  B) 40 .  C) 42 .  D) 44 .  E) 46 .

Rationale: "answer is a : 42 let w be the width , so length is 3 w . therefore : w * 4 w = 768 , solving for , w = 16 , so 3 w - w = 2 w = 2 * 16 = 32"
Answer: A