The roof of an apartment building is rectangular and its length is 5 times longer than its width. If the area of the roof is 720 feet squared, what is the difference between the length and the width of the roof?
Choose the correct choice from the following answers
A) 38 .  B) 40 .  C) 42 .  D) 44 .  E) 48 .

Rationale: "answer is e : 48 let w be the width , so length is 5 w . therefore : w * 5 w = 720 , solving for , w = 12 , so 5 w - w = 4 w = 4 * 12 = 48"
Answer: E