Write a proportion that is equivalent to the statement: If 3 gallons of gasoline cost $5.37, then 8 gallons will cost $14.32.

The whole trick is to keep the same units on the numerator and denominator and have them be related.

gallons1/dollars1 = gallons2/dollars2

fill in the numbers

Now if they want an equation for the cost of n gallons, that's something different