When two variables vary directly they follow the next:
[tex]y=k\cdot x[/tex]k is a constant.
Use the given data: when x=48, y=36 o find the value of k:
[tex]\begin{gathered} 36=k\cdot48 \\ \\ \frac{36}{48}=k \\ \\ k=\frac{3}{4} \end{gathered}[/tex]Then, x and y vary directly following the next equation:
[tex]y=\frac{3}{4}x[/tex]Use the equation above to find x when y=18:
[tex]\begin{gathered} 18=\frac{3}{4}x \\ \\ 18(\frac{4}{3})=x \\ \\ x=\frac{18\cdot4}{3} \\ \\ x=\frac{72}{3} \\ \\ x=24 \end{gathered}[/tex]Then, the value of x when y=18 is x=24