Final answer:
By dividing the initial total cost of $24.50 by 7 gallons, the price per gallon is found to be $3.50. Therefore, for 15 gallons at the same price, Robert will pay $52.50.
Step-by-step explanation:
Robert initially paid $24.50 for 7 gallons of gasoline, signifying that the cost per gallon is the total cost divided by the quantity. To find the cost per gallon, we divide $24.50 by 7, resulting in approximately $3.50 per gallon. With the cost per gallon determined, we can now calculate the cost for 15 gallons by multiplying $3.50 with 15, giving us a total cost of $52.50 for 15 gallons of gasoline, assuming the price per gallon remains the same.