Answer:
Angles in a pentagon add to 540 degrees.
100+80+160+91+x =540
431+x=540
109=x
Hope this helps!
Unsure what you mean by diagonal right triangle
but if you wanted to find the hypothenuse (longest side) of a right triangle, you can apply pythagorean theorem

where c is the hypothenuse
a and b are the other sides
3^3+9=77 if I'm wrong I'm sorry I just guess
529.2 .......................................