A large tank is used to remove a small amount of precipitated solid particles $($impurities$)$ from a saline solution in a steady$-$state process. Normally a saline solution $(20\%$ by mass of salt$)$ is pumped by a single inlet stream into a tank at the rate of $10$ kg$/$min and a single outlet stream is established by pumping from the tank at the same flow rate. The normal operation of the process maintains the constant level, with a total mass in the tank of $1,000$ kg$,$ well below its maximum capacity. At a certain moment $($t $=0)$ an operator accidentally opens a valve, which supplies pure water that constantly flows into the tank at the speed of $10$ kg$/$min$,$ together with $2\mathrm{.}14\mathrm{.}4.$ Resolution te with the saline solution feeding, so the tank level begins to rise.