1. **State the problem:** Solve the equation $ab - ac = qa$ for $q$. 2. **Identify the formula and rules:** We want to isolate $q$ on one side of the equation. The equation is linear in terms of $q$. 3. **Rewrite the equation:** $$ab - ac = qa$$ 4. **Factor the left side:** $$a(b - c) = qa$$ 5. **Divide both sides by $a$ (assuming $a \neq 0$):** $$b - c = q$$ 6. **Final answer:** $$q = b - c$$ This means $q$ is the difference between $b$ and $c$ when multiplied by $a$ on both sides.