1. **State the problem:** We have an equilateral triangle with side lengths of $x + 9$ inches. The perimeter is given by the expression $3(x + 9)$. We want to find which expression also represents the perimeter. 2. **Recall the formula for perimeter of an equilateral triangle:** $$\text{Perimeter} = 3 \times \text{side length}$$ Since each side is $x + 9$, the perimeter is: $$3(x + 9)$$ 3. **Expand the expression:** $$3(x + 9) = 3x + 27$$ 4. **Check the options:** - A: $(x + 9) + (x + 9) + (x + 9) = 3(x + 9)$ which is correct. - B: $(x + 9)(x + 9)(x + 9)$ is the cube of the side length, not perimeter. - C: $3x + 9$ is incorrect because $3 \times 9 = 27$, not 9. - D: $3x + 27$ matches the expanded form. - E: $12x$ is unrelated. 5. **Conclusion:** The expressions that represent the perimeter are A and D. Since the question asks for one expression, the best match is D: $3x + 27$. **Final answer:** $3x + 27$