1. **State the problem:** Solve the equation $m + 13 = 20$ for $m$. 2. **Formula and rules:** To isolate $m$, subtract 13 from both sides of the equation. This uses the property that if $a = b$, then $a - c = b - c$ for any $c$. 3. **Intermediate work:** $$m + 13 = 20$$ Subtract 13 from both sides: $$m + \cancel{13} - \cancel{13} = 20 - 13$$ 4. **Simplify:** $$m = 7$$ 5. **Explanation:** We removed 13 from the left side to leave $m$ alone, and did the same to the right side to keep the equation balanced. The solution is $m = 7$. **Final answer:** $m = 7$