William has a 26-liter glass tank. First, he wants to put some marbles in it, all of the same volume. Then, he wants to fill the tank with some water until its comepletly full. If he uses 85 marbles,

William has a 26-liter glass tank. First, he wants to put some marbles in it, all of the same volume. Then, he wants to fill the tank with some water until its comepletly full. If he uses 85 marbles, he will have to add 20.9 liters of water. What is the volume of each marble? and How much water is necessary if William uses 200 Marbles?