Choice B is the correct answer. Let $s$ be the cost of a small drink and $L$ be the cost of a large drink.

Given: $s = 4$ and $3s + 2L = 18$

Step 1: Substitute $s = 4$: $3(4) + 2L = 18$$12 + 2L = 18$

Step 2: Solve for $L$: $2L = 6$$L = 3$

Solution: One large drink costs $$3$.

Verification: $3(4) + 2(3) = 12 + 6 = 18$ ✓

💡 Strategic Tip: When one variable is given, substitute it immediately to reduce the problem to a single equation.

Choice A is incorrect because$3(4) + 2(2) = 12 + 4 = 16 \ eq 18$.

Choice C is incorrect because$3(4) + 2(4) = 12 + 8 = 20 \ eq 18$.

Choice D is incorrect because$3(4) + 2(5) = 12 + 10 = 22 \ eq 18$.