Choice Dhoice A is the correct answer. When solving $x - a = b$, we add $a$ to both sides.

1. Start with the equation: $x - 18 = 5$
2. Add 18 to both sides: $x = 5 + 18$
3. Calculate: $x = 23$
4. Verify: $23 - 18 = 5$ ✓

The key is recognizing that addition is the inverse operation of subtraction.

Choice Dhoice C is incorrect because this results from subtracting 18 from 5: $5 - 18 = -13$. This applies subtraction twice instead of using the inverse operation (addition).

Choice Dhoice D is incorrect because this is the absolute value of Choice Dhoice C. Some students might calculate $5 - 18 = -13$ and then drop the negative sign, giving 13.

Choice Dhoice C is incorrect because this is the negative of the correct answer. If you mistakenly subtract instead of add and then apply a negative: $-(5 + 18) = -23$.