Answer:
We have two fruits so we have following choices to make exactly 4 cups of fruits:
Blueberry Orange
0 4
1 3
2 2
3 1
4 0
In case 1: when she is using 4 cup of oranges so no need of blueberry.
In case 2: when she is taking 3 cup of oranges she will use 1 cup of blueberry to get exactly 4 cups of fruits.
case 3: when she is taking 2 cup of oranges she will use 2 cup of blueberries to get exactly 4 cups of fruits.
case 4: when she is taking 1 cup of orange she will use 3 cup of blueberries to get exactly 4 cups of fruits.
case 5: when she is taking 0 cup of orange she will use 4 cup of blueberries to get exactly 4 cups of fruits.
