Choice Choice C is the correct answer. This is a classic two-step equation. We need to undo addition first, then multiplication.

1. Start with the equation: $2x + 5 = 15$
2. Subtract 5 from both sides: $2x = 15 - 5$
3. Simplify: $2x = 10$
4. Divide both sides by 2: $x = \frac{10}{2}$
5. Simplify: $x = 5$
6. Verify: $2(5) + 5 = 10 + 5 = 15$ ✓

💡 Order of Operations: When solving, we reverse PEMDAS. We deal with addition/subtraction before multiplication/division.

Choice Choice D is incorrect because this results from forgetting to divide by 2 after subtracting: $2x = 10$, so student thinks $x=10$.

Choice Choice B is incorrect because this results from adding 5 instead of subtracting: $15 + 5 = 20$, then $20/2 = 10$. Or perhaps dividing 15 by 2 first.

Choice Choice B is incorrect because this results from adding 5 to 15 to get 20, and then maybe forgetting to divide.