Please help me with this question ​

Adam plans to choose a video game from the section of the store where everything is 75% off. he writes the expression d-0.75d to find the sale price of the game if the original price is d dollars. gena correctly writes another expression, 0.25d, that will also find the sale price of the game if the original price is d dollars. use the drop down menus to explain each part of adams and rena's expression

How do you solve a question like this?

You paid 28.00 for 8 gallons of gasoline. how much would you pay for 15 gallons of gasoline?