By leg I guess you mean any side except the hypotenuse. This is an isosceles right-angled triangle, because two angles are the same. Therefore two sides have the same length, too. The Pythagorean rule applies: the square on the hypotenuse is equal to the sum of the squares on the other two sides. The side length is 6 inches, which means that the other side is also 6 inches. 6 inches squared is 36 sq inches added to the square of the other side makes 72 sq inches. The hypotenuse is the square root of 72 sq in=8.4583 inches approx.