Answer
When $x=40$, the value of $y$ is $12$.
Work Step by Step
$y$ varies directly so its equation is of the form $y=kx$.
When $x=30$, $y=9$. Substitute these values into $y=kx$ to obtain:
$y=kx
\\9=k(30)
\\\frac{9}{30}=\frac{k(30)}{30}
\\\frac{3}{10}=k$
Thus, the direct variation is $y=\frac{3}{10}x$.
To find the value of $y$ when $x=40$, substitute $40$ to $x$ in the equation above to obtain:
$y=\frac{3}{10}x
\\y=\frac{3}{10}(40)
\\y=\frac{120}{10}
\\y=12$
