Answer: 15
(b)
Step-by-step explanation:
You can separate a square into two different 45-45-90 degree triangles.
Where x = 15, and the diagonal would be the hypotenuse.
So, here you can use the Pythagorean Theorem to find the hypotenuse to use 45-45-90 triangle theorem where they hypotenuse is always x times
So, the diagonal would be 15