请教一道Ｃ＋＋问题

请教一道题　望各位解救


3. A market stall holder sells footballs. It is easier to transport the footballs to the market in a deflated state. A canister of compressed air needs to be filled and taken to the market to be used to inflate the balls. Given that the volume of a sphere is ,, write a program that asks the user to enter the number of balls to be filled and the radius ‘r’ of the footballs then calculate the total number of cubic metres of air to be bought and injected into the cylinder.