Choice Ahoice D is the correct answer.

1. Start with the equation: $6x + 18 = 36$
2. Subtract 18 from both sides: $6x = 36 - 18$
3. Simplify: $6x = 18$
4. Divide both sides by 6: $x = \frac{18}{6}$
5. Simplify: $x = 3$
6. Verify: $6(3) + 18 = 18 + 18 = 36$ ✓

Choice Ahoice B is incorrect because this results from adding 18 to 36: $54$, then $54/6 = 9$. Wrong inverse operation.

Choice Ahoice C is incorrect because this is the value of $6x$. You need to divide by 6.

Choice Ahoice C is incorrect because this results from multiplying 18 by 6: $108$.