So the range is that combined sugar and chocolate chips you can have [1,10/3] cups.
So far, you have already poured in three and three quarters which in improper fractions is 15/4. Multiply the y-range of the combined with 4, to get this:
12/12 => 40/12. Then multiply 15/4 by three to get 45/12. Clearly you see this that more cups of sugar than the limit is poured. you can only go to 40/12, but 45/12 is just sugar, so no chocolate chips can be added
