Answer:
900 large boxes were sold, and 750 small boxes.
Step-by-step explanation:
This question can be solved by a system of equations.
I am going to say that:
x is the number of large boxes of cookies sold.
y is the number of small boxes of cookies sold.
A total of 1,650 boxes of Girl Scout cookies were sold last week.
This means that

So

Each large box cost $3.50 and each small box cost $2.00. The Girl Scout group earned $4,650.
This means that

Since 






900 large boxes were sold, and 750 small boxes.