To determine the cost of one gallon of gasoline, you can set up a proportion. The total cost of gasoline is $45.50 for 15 gallons.
The proportion can be set up as follows:
\[ \text{Cost per gallon} = \frac{\text{Total Cost}}{\text{Total Gallons}} = \frac{45.50}{15} \]
Now, performing the division:
\[ \text{Cost per gallon} = \frac{45.50}{15} \approx 3.0333 \]
Rounding that to the nearest hundredth, you get:
\[ \text{Cost per gallon} \approx 3.03 \]
So the answers are:
- The proportion used to determine the cost for one gallon of gasoline is \( \frac{45.50}{15} \).
- The cost of gasoline per gallon is \( \mathbf{3.03} \) per gallon.