Answer
$15$
Work Step by Step
Recall:
If $y$ varies directly as $x$, then $y=kx$ where $k$=constant of variation.
When $x=1$, the value of $y$ is $5$.
Substitute these values into the equation above to obtain:
\begin{align*}
y&=kx\\\\
5&=k(1)\\\\
5&=k\\\\
\end{align*}
Thus, the direct variation is $y=5x$.
To find $y$ when $x=3$, substitute $3$ to $x$ to obtain:
\begin{align*}
y&=5x\\
y&=5(3)\\
y&=15
\end{align*}
