Choice C is the correct answer. Let $f$ = floor seats and $b$ = balcony seats.

System: $\begin{cases} f + b = 400 \\ 75f + 45b = 22500 \end{cases}$

Step 1: From first: $b = 400 - f$

Step 2: Substitute: $75f + 45(400 - f) = 22500$$75f + 18000 - 45f = 22500$$30f = 4500$$f = 150$

Solution: 150 floor seats (and 250 balcony seats)

Verification: $150 + 250 = 400$ ✓ and $75(150) + 45(250) = 11250 + 11250 = 22500$ ✓

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

Choice A is incorrect because $75(100) + 45(300) = 7500 + 13500 = 21000 \ eq 22500$.

Choice B is incorrect because $75(125) + 45(275) = 9375 + 12375 = 21750 \ eq 22500$.

Choice D is incorrect because $75(175) + 45(225) = 13125 + 10125 = 23250 \ eq 22500$.