1. **State the problem:** We have a triangle with two known angles, 37° and 73°, and we need to find the unknown angle $a$. 2. **Formula used:** The sum of the interior angles of any triangle is always 180°. This means: $$a + 37 + 73 = 180$$ 3. **Calculate $a$:** $$a = 180 - 37 - 73$$ 4. **Simplify:** $$a = 180 - 110 = 70$$ 5. **Answer:** The value of angle $a$ is 70°. This works because the angles in a triangle always add up to 180°, so subtracting the known angles from 180° gives the missing angle.