\[y = \frac{1}{5}x^{2}\ и\ y = 20 - 3x\]
\[\frac{1}{5}x^{2} = 20 - 3x\]
\[\frac{1}{5}x^{2} + 3x - 20 = 0\ \ \ \ \ \ | \cdot 5\]
\[x^{2} + 15x - 100 = 0\]
\[x_{1} + x_{2} = - 15;\ \ \ \ x_{1} \cdot x_{2} = - 100\]
\[x_{1} = - 20;\ \ \ x_{2} = 5.\]
\[y_{1} = \frac{1}{5} \cdot 400 = 80;\]
\[y_{2} = \frac{1}{5} \cdot 25 = 5.\]
\[Точки\ пересечения\ графиков:\]
\[( - 20;80);\ \ (5;5).\]