4 servings of stew has 2 potatoes and 4 celery sticks
Divide all those numbers by 2.
2 servings of stew has 1 potato and 2 celery sticks
Multiply all those numbers by 3.
6 servings of stew has 3 potatoes and 6 celery sticks.
In 6 servings, there are 3 potatoes and 6 celery sticks.