the length of each leg is unknown is first you would have to figure out how long each leg is, one leg is 30ft because of the 30ft on the other side. But since we don't know how long the top is we have to do 70 - 30 which is 40 now that we have both legs we can use the Pythagorean theorem 30^2 + 40^2 = c^2 the answer is 2500 and if we square it we get 50 hope this helps :)