I've drawn the cylinder with radius 3 dm but I'm not exactly sure what they mean by movable piston.
I guess it is just a part sticking out with height h?
I've also gotten the area of the circular base - A= pi * r^2. = pi * 9 = 28 dm^2.
So volume of the cylinder is then 280 liters.
Would the answer then by V = 280 - 2T?