Urgent please help..

Because both angle are congruent, the triangle is isoceles (45° - 45° - 90°) which means the two sides besides the hypotenuse are the same.

Therefore if one side other than the hypotenuse is 6, than x must be 6 too.

x = 6

this may not be at all, but i use the same website you're using for school, and if i'm stuck doing one of these i try to look for it on the section.