The problem states that there are $s$ students in an art club. Each student painted 4 pictures. We need to write an expression that represents the total number of pictures painted.

1. Problem Description

The problem states that there are $s$ students in an art club. Each student painted 4 pictures. We need to write an expression that represents the total number of pictures painted.

2. Solution Steps

Let the number of students be $s$.

Each student painted 4 pictures.

The total number of pictures painted is the number of students multiplied by the number of pictures each student painted.

Therefore, the total number of pictures painted is $4 \times s$, which can be written as $4s$.

3. Final Answer

4s