Answer
$y=1.2$
Work Step by Step
Recall:
If $y$ varies directly as $x$, then $y=kx$ where $k$=constant of variation.
When $x=10$, the value of $y$ is $3$.
Substitute these values into the equation above to obtain:
\begin{align*}
y&=kx\\\\
3&=k(10)\\\\
3&=10k\\\\
\frac{3}{10}&=\frac{10k}{10}\\\\
0.3&=k\end{align*}
Thus, the direct variation is $y=0.3x$.
To find $y$ when $x=4$, substitute $4$ to $x$ to obtain:
\begin{align*}
y&=0.3x\\
y&=0.3(4)\\
y&=1.2
\end{align*}
