Right triangle always has the Hypotenuse as the longest side which means the other two in this case are 20 m long. We can calculate the length of hypotenuse by using Pythagoras Theorem
a = (b^2 + c^2)^0.5
a = (20^2 + 20^2)^0.5
a = 28.28
Thus Perimeter = a + b + c = 28.28 + 20 + 20 = 68.28 m
