The perimeter of a square-shaped piece of paper is 20 cm shorter than the height of a computer screen. How many cm is the height of the screen if the side of the square paper is 20 cm?
The perimeter of a square is found by 4*side, which means the square paper has a perimeter of 4*20 = 
<gadget id="calculator">4*20</gadget>
<output>80</output>
80.
Since the perimeter of the square is 20 cm shorter than the height of the computer screen, the height of the computer screen is 20+80 = 
<gadget id="calculator">20+80</gadget>
<output>100</output>
100cm.

<result>100</result>