I'm sorry but the solution you proposed was a bit hard to follow, so I'll just post my solution: we convert "2 and 1/2" to a single fraction:
![2+(1)/(2) = (4)/(2)+(1)/(2)=(5)/(2)](https://img.qammunity.org/2020/formulas/mathematics/high-school/57nbn5uzwbquurmpszf3cvv5fzzrh4pgfl.png)
So, we know that 5/2 gallons cost 60 dollars, which means
![(5)/(2)g=60](https://img.qammunity.org/2020/formulas/mathematics/high-school/7xw0tn77c1nyxsnt8eyp5aywij2jwlo1nk.png)
To find the cost of a single gallon, we have to solve the equation for g:
![g = 60\cdot (2)/(5) = 24](https://img.qammunity.org/2020/formulas/mathematics/high-school/iiza1nstsb92q49d6wxr1g2lq7bt1g238w.png)