If y varies directly with x, that means there is going to be a constant that connects both the x and y variable.
[tex]\begin{gathered} \text{When x=15, and y=40, then} \\ k=\frac{y}{x} \\ k=\frac{40}{15} \\ k=\frac{8}{3} \\ \text{Therefore, the equation is going to be;} \\ y=\frac{8}{3}x \end{gathered}[/tex]The appropriate direct variation equation is stated above, and that is;
y = 8/3x
