Problem: the roof of an apartment building is rectangular and its length is 4 times longer than its width . if the area of the roof is 900 feet squared , what is the difference between the length and the width of the roof ? 
Options: ['a ) 38 .', 'b ) 40 .', 'c ) 42 .', 'd ) 44 .', 'e ) 45 .']
e