So if you need 1/2 cup for a 3-layer, then it means that you need a third of that for a one-layer. you need to divide 1/2 by 3. It is easier to get that if you use another form of 1/2, for example 3/6. In this case you simply divide this by 3 and you'll get 1/6.
Juan’s lunch would have costed less if he paid separately. his lunch is 5.25 the bill 37.20 37.20 / 5 $7.44 each kid 7.44 - 5.25 = 2.19 $2.19 less if he paid separately