What is the value of x? also have 2 more questions if anyone can !

The correct answer is:  [D]:  " 8√2 " .


Since this is a "45-45-90" triangle; 

and we are given that one of the "non-hypotenuse sides" is "8" ; 
 
The other non-hypotenuse side is "8"; and the hypotenuse, "h", (as denoted in the image), is equal to: "8√2" 

Note:  The rule for "45-45-90" triangles:  the sides are "x, x, and x√2" ; in which: "x√2" is the hypotenuse.