According to the given image, the function consists of multiplying the input value by 3, then we sum 3 to get the output value. So, the equation for this function would be

Now, we solve the equation for x, first, we subtract 3 on each side.

Then, we divide the equation by 5.

We use each output value to find each input value.
For y = 13.

The first input is 2.
For y = 28.

The second input is 5.
For y = 33.

The third input is 6.
For y = 48.

The fourth input is 9.
Therefore, the input values are 2, 5, 6, and 9.