Yuri O. answered 02/03/21
16 years online, 464 former SAT problems drilled down
10: It is isosceles triangle (both angles 45 degrees).
V = 6√2
U = √144 = 12 ← from Pythagorean theorem
12: Isosceles triangle.
x = y
√2x2 = 18√2, x√2 = 18√2, x = 18
13: Isosceles triangle.
x = y
√2x2 = 15, x = 15/√2
14: Isosceles triangle.
x = y
x =20/√2