When josh babysits, he charges a flat fee of $4 plus an hourly rate or r dollars

I think what you are looking for is the equation on how this could be displayed.

The baseline is 4, and the hourly rate of r.

This can be shown by:

4 + r = cost

The question doesnt seem to be repeated. From here, I'm just going to assume the hours he worked is 4. Heres what the equation would look like.

4x + 4 = r

r = total money earned

x = cost per hours worked

The plus 4 is the flat fee he charges,