A triangle is both right-angled and isosceles, so apart from its right angle its two remaining angles are equal. Enter the number of degrees in each of those two equal angles.

Explication

The right angle takes 90 of the 180 degrees, leaving 90 degrees to be split evenly between the pair, so each of them is 45. Entering 60 borrows the value from a triangle with three matching angles, and such a triangle has no room for a right angle at all.