4. Решим уравнение:
$$ \frac{v}{6} - v = -3.6 $$ $$ \frac{v}{6} - \frac{6v}{6} = -3.6 $$ $$ \frac{v-6v}{6} = -3.6 $$ $$ \frac{-5v}{6} = -3.6 $$ $$ -5v = -3.6 \cdot 6 $$ $$ -5v = -21.6 $$ $$ v = \frac{-21.6}{-5} $$ $$ v = 4.32 $$
Ответ: v = 4.32