A tank contains $5000\text{L }$ of pure water. Brine that contains $40\text{g }$ of salt per liter of water is pumped into the tank at a rate of $25\text{L/min}.$ Answer the following questions.

1. Find the function for concentration of salt (in grams per liter) after $t$ minutes.
Function: $C(t) =$

2. What number does the concentration approach as $t \longrightarrow \infty$?