To find the maximum number of snacks \( s \) that Emma can buy, we know that each snack costs $3 and she has a maximum of $18 to spend. We can set up the inequality based on this information:
\[ 3s \leq 18 \]
This means that the total cost of the snacks (which is \( 3 \times s \)) must be less than or equal to $18.
So, the correct response is:
3s ≤ 18