Energy required needed to turn 0.2kg of aluminium from 15° to 40°? (shc)

To find the height of the TV you first need to realize that the question is giving you dimensions for a triangle. 

Every triangle has a hypotenuse and two sides. To find the hypotenuse you square both sides, add them, and then square root. So to find one of the sides you get the hypotenuse, square it, and subtract the square length of the given side. 

The equation is 25^2-20^2.
Which if simplified is 625-400, the then solution is going to be 225. 
You next will square root 225, 225^(1/2). Which your answer should be 15 inches for the missing side length.