## Precalculus (6th Edition) Blitzer

$y=117$
To find out the solution we need to follow the 3-step procedure: Step (1). As $y$ varies directly as $x$ varies, we have $y=kx$ Here $k$ is a constant. Step (2) Substitute $x=5$ and $y=45$ in $y=kx$ to find the value of k. \begin{align} & 45=k\left( 5 \right) \\ & \frac{45}{5}=k \\ & k=9 \\ \end{align} Step (3). Substitute $k=9$ and x = 13 in $y=kx$. \begin{align} & y=9\times 13 \\ & y=117 \\ \end{align}