While walking through a market on vacation, you notice a small stand selling cameras. A camera-and-case set is selling for £310. The seller tells you that the camera costs £300 more than the case itself and that the case costs the price of the set minus the cost of the camera.
You decide you'd rather wait on buying a camera and opt to just buy the case alone. You hand the seller a £100 bill and see his eyes light up.
How much change should you be getting back?
Remember, you have 3 hints!