Reduce the fraction $\frac{9}{15}$ to lowest terms by extracting and canceling out $3$.
$$\frac{3}{5}-\frac{4}{5}\times \frac{u}{6}$$
Multiply $\frac{4}{5}$ times $\frac{u}{6}$ by multiplying numerator times numerator and denominator times denominator.
$$\frac{3}{5}-\frac{4u}{5\times 6}$$
Cancel out $2$ in both numerator and denominator.
$$\frac{3}{5}-\frac{2u}{3\times 5}$$
Multiply $3$ and $5$ to get $15$.
$$\frac{3}{5}-\frac{2u}{15}$$
To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $5$ and $15$ is $15$. Multiply $\frac{3}{5}$ times $\frac{3}{3}$.
$$\frac{3\times 3}{15}-\frac{2u}{15}$$
Since $\frac{3\times 3}{15}$ and $\frac{2u}{15}$ have the same denominator, subtract them by subtracting their numerators.
