\[f(x) = \frac{1}{5}x^{2} - 6x\]
\[f(5) = \frac{1}{5} \cdot 25 - 6 \cdot 5 = 5 - 30 = - 25.\]
\[f( - 1) = \frac{1}{5} \cdot 1 - 6 \cdot ( - 1) = 0,2 + 6 = 6,2.\]