# How do you multiply (7x)/(5x+15)*(x+3)/(8)?

$\setminus \frac{7 x}{40}$
Observe that you can factor a $5$ from the denominator of the first fraction: $5 x + 15 = 5 \left(x + 3\right)$. Rewriting that fraction with this factorization and cross-simplifying, you have
$\setminus \frac{7 x}{5 \setminus \cancel{\left(x + 3\right)}} \cdot \setminus \frac{\cancel{x + 3}}{8} = \setminus \frac{7 x}{5 \cdot 8} = \setminus \frac{7 x}{40}$