AC is the hypotenuse of triangle ABC.
Because the length is 6√2 and angle A is 45 degrees, we know the length of both sides is 6.
This means AB is 6, which it the hypotenuse of triangle BCD.
Using cos(angle) = adjacent leg / hypotenuse we can find x:
cos(60) = X / 6
x = 6 * cos(60)
x = 3
