So the inside triangle has two equal sides. To find these angles you would do the degrees of a triangle (180) minus the known value and then divided by two.
so it is: 180-126/2 which gives you 27 degrees.
this means the n value is 27.
to find m, you have to take away 90 degrees and the n value from 180.
so it is: 180-90-27 which gives you 63 degrees.
now you must take the smaller angle from 63 degrees to find m.