First of all, you must find the length of the side to add with 36 to equal 100. This would give you 64. So once you do that, you can do pythagorean theorem to find the length of x. This would give you 64^2 + 48^2 = x^2. Once you have this equation, you square your terms to get; 4,096 + 2,304 = x^2. After you add them you will now have 6,400 = x^2. Once you have this, you will need to do the square root of both sides of the equation; sqrt(6400) = x. This gives you x = 80.
