Okay, so it says that per every 4 ounces you take in 50 calories. So 12 divided by 4 gives you 3, this is done to help you figure out how many times he drinks the 50 calories. Since he did it 3 times that means you multiply 50 and 3 which gives you 150 calories as his ending calorie intake of the juice. Hopes this helps you to understand the question!