Sara brought a total of 5 cartons of blackberries. Since it said that Sara brought 6 cartons and you know that the cost of the blackberries are $2, you multiply 6 with 2 but its 12. But if Sara brought 2 cartons of raspberries it will be $3. Now you subtract 6 with 2 since you used 2 cartons on raspberries and now multiply $2 with 4 and get 8. 8+3=11, which is exactly how much she needs. This means that Sara brought 4 cartons of blackberries.
