One of the rules of the system is that people over 18 years old only get 60% as much food as people under 18 years old get. (since younger people need more calories because their bodies are still growing)
You get a shipment of food that is to be given to a group comprised of 20 people over 18 and 20 people under 18. In other words an equal amount of people under and over 18.
What percentage of the food do you give to the people over 18?