How could a teenager obtain a days worth of calcium

One could drink milk or take yogurt.

Explanation:

I found this statement to back it up:

Children and teenagers between the ages of 9 and 18 should aim for 1,300 milligrams per day, which is about 4 servings of high-calcium food or drinks. Each 8-ounce glass of milk (whether 1%, 2%, or whole) and each cup of yogurt has about 300 milligrams of calcium.

Hope I helped :)