In triangle ABC, angle B is 90° and angle A is 45° => triangle ABC is Isosceles triangle. That means side AB = BC
Also, side AC² = AB² + BC² = 2BC²
(6√2)² = 2BC² => 36*2
BC = 6
In triangle BCD, angle D is 90° and angle B is 60° => triangle BCD is semi Equilateral triangle. That means side BD = ½BC = 6/2 = 3 which is the value of X.
Good luck