What you have here is a simple algebraic equation. So, what you have to do is take out the numbers they give you and put it into an equation.
So let us refer to rolls of gift wrap as 'x'. So, you need 50x + $125 (from the chocolate) to = $400 in total sales. The equation you get is
50x + 125 = 400
The next step is to subtract 125 from both sides making it:
50x = 275
Now you divide both sides by 50 to get x as a single variable:
X = 5.50
So each roll of wrapping paper costs $5.50.