Answer:
if I did my math right it's 45 if not please fix me
Explanation:
First thing is the the sides are congruent meant the angles have to be the same.
Next is the box indicates 90°.
Last thing is that every triangle is 180°
so if I did this right the equation is 2x+90=180
and using algebra in this you eliminate the 90 by subtract because - is the opposite of + which cancels itself and leaving the total with 90.
Then divide the 90 by 2 as it cancels out 2x leaving the answer with x=45
I hope this helps you