Variable $\nu $ cannot be equal to $0$ since division by zero is not defined. Multiply both sides of the equation by $60\nu $, the least common multiple of $\nu ,15,-20$.
$$60=60\nu \times \frac{1}{15}+3\nu $$
Multiply $60$ and $\frac{1}{15}$ to get $\frac{60}{15}$.
$$60=\frac{60}{15}\nu +3\nu $$
Divide $60$ by $15$ to get $4$.
$$60=4\nu +3\nu $$
Combine $4\nu $ and $3\nu $ to get $7\nu $.
$$60=7\nu $$
Swap sides so that all variable terms are on the left hand side.
