Answer:
Pythagoras Therom a^2 + b^2= C^2
Opposite the right angle is x at the bottom which is the hypotenuse. you only need to work out the bottom triangle so forget the top.
18/2=9 for the bottom length.
9^2 + 20^2 = 481^2 (opposite of squaring)
square root 481 = 21.9317121 rounded up would be 22cm x= 22cm
