To determine which store has a better buy for a gallon of gasoline, we should compare the cost per gallon for both stores based on the data provided.
Store A:
- At 5 gallons, the cost is $20, so the cost per gallon is \( \frac{20}{5} = 4.00 \) per gallon.
- At 10 gallons, the cost is $40, so the cost per gallon is \( \frac{40}{10} = 4.00 \) per gallon.
- At 15 gallons, the cost is $60, so the cost per gallon is \( \frac{60}{15} = 4.00 \) per gallon.
The cost per gallon in Store A is consistently $4.00.
Store B:
- At 5 gallons, the cost is $18.75, so the cost per gallon is \( \frac{18.75}{5} = 3.75 \) per gallon.
- At 10 gallons, the cost is $37.50, so the cost per gallon is \( \frac{37.50}{10} = 3.75 \) per gallon.
- At 15 gallons, the cost is $56.25, so the cost per gallon is \( \frac{56.25}{15} = 3.75 \) per gallon.
The cost per gallon in Store B is consistently $3.75.
Conclusion: Store B has a lower cost per gallon ($3.75) compared to Store A ($4.00). Thus, Store B offers the better buy for a gallon of gasoline.
So the answer is 2 for Store B.