A square mirror has exactly half the area of the rectangular wall on which it is hung. If each side of the mirror is 21 inches and the width of the wall is 28 inches, what is the length of the wall, in inches?  Choose the correct choice from the following answers: A) 21.5 B) 31.5 C) 41.5 D) 61.5 E) 71.5

Rationale: "since the mirror is 42 inches in all sides , it must be a square . area of a square is a = a ^ 2 ; 21 ^ 2 = 441 . area of rectangle is double of that 2 * 441 = 882 . now a = lw and we need find w so a / l = w ; 882 / 28 = 31.5 answer ! answer is b"
Answer: B