The correct choice is (c) 35.8 units
To elaborate: Since here distance from side view and top view is asked for that we need the distance between the front view and side view (12+9); front view and top view (9+20)and these lines which form perpendicular to each other gives needed distance, answer is square root of squares of both the distances √(21^2+29^2 ) = 35.80 units.