Final answer:
Sophie's total expenditure is calculated by adding the car rental cost and the gasoline cost, then subtracting half of the car rental cost that her friend Melody contributed.
Step-by-step explanation:
The student is asking how to determine the total amount that Sophie spent. Sophie paid m dollars to rent a car and also bought $25 worth of gasoline. Her friend Melody pays for half the cost of the car rental only. The expression to calculate Sophie's total expenditure would be m + $25 - (m/2). This represents the car rental cost plus the cost of gasoline minus the half of the car rental cost that Melody paid.