100 - 36 = 64 - The larger segment of hypotenuse
Sqrt(64 * 36) = 48 - which is the altitude (The red dotted line).
In the smaller right triangle to the RHS, will use Pythagoras's Theorem to solve for x.
x^2 =36^2 + 48^2
x^2 = 3600 Take the square root of both sides
x = 60