The first question is simple. Draw a picture and compare it, and you will understand ∠ nmb = (180-∠ a)/2-(90-∠ a) =15.

According to this law, ∠ nmb = (180-∠ a)/2-(90-∠ a) = 35.

The third problem is that the bigger ∠A, the bigger ∠NMB.

Fourth, if ∠A is an obtuse angle, then the extension line of the intersection of the perpendicular line between AB and AC is at N, and the triangle will be opposite to the original triangle after drawing. The bigger a is, the smaller NMB is.