Use the following format for the display out put.

// Display the result

cout << "Enter start mileage ";

//get and store mileage from user

cout<<"Enter end mileage";

//get and store mileage from user

cout<<"Enter gas used"<

//get and store gas used from user.

cout << " Your car gets " << mileage << " miles per " << "gallon. ";

3 Miles Per Gal is what they want the end result to be

for c++