Please show all the steps and what theorems you used.

Water is continuously added to a large silver tank that initially contains so amount of salt. The volume of water-salt solution in the tank is kept constant by keeping the same rate of outflow as inflow. As well, the amount of salt, denoted s, in the tank depends on the amount of water, denoted w, that has been pumped into the tank, and this relationship is given by d's where V is the volume of the water-salt solution. Find the amount of water that must be added into the tank to eliminate 25% of the initial amount of salt. Note: all quantities are assumed to be positive