what is the measure of angle 1?
m∠1=°.

Ok so lets first determine all the angles of the triangle.
Given:
Angle A = 90
Angle B = 45
Angle C = ?

If we add up all the angles of any triangle, we should get 180 degrees.
Therefore, Angle C = 90 (angle A) - 45 (angle B) = 45 degrees.

Since there was a ray drawn from A through C the exterior angle of angle C is angle 1.
Any straight line should equal to 180 degrees.
Therefore, angle 1 = 180 - angle C = 135

angle 1 = 135 degrees

No because if you do the higher number minus the lower number you will get a positive. if you do it the other way around you will get a negative number