Question

Two angles in a triangle add up to 135 degrees what is the size of the third angle?

Answer 1

This question is checking to see if you remember what the three angles
of any triangle always add up to.  Apparently you don't, or you would not
need to go out looking for somebody who does.

The three angles inside every triangle always add up to  180° .

If two of them add up to  135° , then that leaves

                           (180° - 135°) =  45° .

for the one remaining angle.