Subtract $21.75 from $26. That is the amount Zing still needs to fill his tank.

You can solve this problem by adding, subtracting, multiplying, or dividing. If you subtract, you can calculate how many more times Zing must walk the dog by subtracting $3.75, the amount Zing gets for walking the dog, from the amount he still needs. How many times do you need to subtract? That is your answer.