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°
