Apply direct proportion
The question discribe a direct proportion. As one quantity increase, the other increase and as it decrease, the other also decrease.
15 minutes = 1/5 gallons
60x = y
Next express each equation into ratio and equate.
[tex]\begin{gathered} \frac{15}{\frac{1}{5}}\text{ = }\frac{60x}{y} \\ \text{cross multiply} \\ 15y\text{ = }\frac{1}{5}\text{ x 60x} \\ 15y\text{ = 12x} \end{gathered}[/tex]