1. **State the problem:** Calculate the result of the subtraction $42 - 18$. 2. **Recall the subtraction operation:** Subtraction means taking away the second number from the first number. 3. **Perform the subtraction:** $$42 - 18 = 24$$ 4. **Explain the result:** When you subtract 18 from 42, you are left with 24. **Final answer:** $24$