Choice A is the correct answer. Let $a$ = adult tickets and $s$ = student tickets.

Step 1: Set up the system: $\begin{cases} a + s = 300 \\ 12a + 8s = 2800 \end{cases}$

Step 2: From first equation: $s = 300 - a$

Step 3: Substitute: $12a + 8(300 - a) = 2800$$12a + 2400 - 8a = 2800$$4a = 400$$a = 100$

Solution: 100 adult tickets (and 200 student tickets)

Verification: $100 + 200 = 300$ ✓ and $12(100) + 8(200) = 1200 + 1600 = 2800$ ✓

💡 Strategic Tip: Revenue problems: tickets × price = total revenue.

Choice B is incorrect because $12(150) + 8(150) = 1800 + 1200 = 3000 \ eq 2800$.

Choice C is incorrect because $12(125) + 8(175) = 1500 + 1400 = 2900 \ eq 2800$.

Choice D is incorrect because $12(175) + 8(125) = 2100 + 1000 = 3100 \ eq 2800$.