Write down, but do not solve, the equation for the amounts x(t), y(t) lbs. of salt i \frac{d x}{d t}=f(x, y), \quad \frac{d y}{d t}=g(x, y) f(x, y)=? \bigcirc_{2}-\frac{4 x}{20}+\frac{2

y}{10} 1-\frac{2 x}{20}+\frac{2 y}{10}