A very large tank initially contains $100\text{L}$ of pure water. Starting at time $t=0$ a solution with a salt concentration of $0.3\text{kg/L}$ is added at a rate of $6\text{L/min}.$ The solution is kept thoroughly mixed and is drained from the tank at a rate of $4\text{L/min}.$ Answer the following questions.

---

1. Let $y(t)$ be the amount of salt (in kilograms) in the tank after $t$ minutes. What differential equation does $y$ satisfy? Use the variable $y$ for $y(t).$
Answer (in kilograms per minute): $\displaystyle \frac{dy}{dt} =$

2. How much salt is in the tank after $20$ minutes?
Answer (in kilograms):

---