1. **State the problem:** Find the value of the missing angle $x$ in each triangle given two angles. 2. **Formula used:** The sum of the interior angles of a triangle is always $180^\circ$. So, for angles $A$, $B$, and $C$, we have: $$A + B + C = 180^\circ$$ 3. **Solve each part:** **a)** Given angles: $50^\circ$, $70^\circ$, and $x^\circ$. $$50 + 70 + x = 180$$ $$120 + x = 180$$ $$x = 180 - 120 = 60$$ **b)** Given angles: $90^\circ$, $45^\circ$, and $x^\circ$. $$90 + 45 + x = 180$$ $$135 + x = 180$$ $$x = 180 - 135 = 45$$ **c)** Given angles: $30^\circ$, $110^\circ$, and $x^\circ$. $$30 + 110 + x = 180$$ $$140 + x = 180$$ $$x = 180 - 140 = 40$$ 4. **Final answers:** - a) $x = 60^\circ$ - b) $x = 45^\circ$ - c) $x = 40^\circ$