Firstly, let's find out how many peanutt balls we need.
Since there are 120 children, and since each will receive 4 peanut butter balls, we need 4 times as many:

Since each receipt makes 40 peanut butter balls, we can divide the total by 40 to know how many receipt quantities we will need:

That is, we will need 12 times the quantities in one receipt to make all the peanut butter balls we need.
1 receipt need 1 1/2 cups of peanut butter, that is the same as one and one half, or 1.5.
12 times that is the total we will need:

That is, we need a total of 18 cups of peanut butter, third alternative.