Set 3: Systems of Equations (Intermediate)

Choice D is correct. Choice D is the correct answer. Let $a$ = adults and $c$ = children. System: $\begin{cases} a + c = 180 \\ 15 a + 9 c = 2100 \end{cases}$ Step 1: From first: $c = 180 - a$ Step 2: Substitute: $$$15a + 9(180 - a) = 2100$15a + 1620 - 9 a = 2100$6a = 480$a = 80$15(80) + 9(100) = 1200 + 900 = 2100$ ✓ Strategic Tip: Revenue = tickets × price.