3.
Find m21.
1
140°
50°

Explanation:

step 1. let called the acute angles inside the triangle <1 and <2.

step 2. <2 +140 = 180 (supplementary angle)

step 3. <2 = 40°

step 4. <1 + <2 + 90 = 180. (interior angles of a triangle = 180°)

step 5. <1 + 40 = 90

step 6. <1 = 50°