[tex]\begin{gathered} y\text{ varies directly as x means that} \\ y=mx \\ \text{where m is a constant of proportionality.} \\ We\text{ know that when x=5, y =12, hence} \\ 12=m(5) \\ m=\frac{12}{5} \\ \text{Therefore, the euqtion searched is} \\ y=\frac{12}{5}x \\ \text{Now, we must find x when y=36. Then} \\ 36=\frac{12}{5}x \\ \frac{36}{12}=\frac{x}{5} \\ 3=\frac{x}{5} \\ 3\cdot5=x \\ x=15 \end{gathered}[/tex]
