1. **State the problem:** Solve for $a$ in the equation $a - b = 4$. 2. **Formula and rules:** To isolate $a$, add $b$ to both sides of the equation. This uses the addition property of equality which states that adding the same number to both sides keeps the equation balanced. 3. **Intermediate work:** $$a - b = 4$$ Add $b$ to both sides: $$a - b + b = 4 + b$$ Simplify: $$a = 4 + b$$ 4. **Explanation:** We moved $b$ to the right side by adding it to both sides, which isolates $a$ on the left side. The solution expresses $a$ in terms of $b$. **Final answer:** $$a = 4 + b$$