all sides of a triangle add up to 180 degrees. looking at the triangle, the angles that we are provided are E and F. E is 90 degrees, and F is 45 degrees. If you add those together, we get 135. then, subtract 180 from 135, and you get your answer, which is 45 degrees.
also, it says on the smaller triangle in the bottom left.
Since there's a triangle, the only possible answer would be 45. If you add 45°+45°+90° it equals to 180°, which is the sum of angles in all triangles. I don't think I explained this very well but hope it helps :)
