Because the orange paper comes in packs of 6, we know that they have to make at least 6. Fortunately, the blue paper comes in packs of 3, so they can buy 2 packs of blue paper and 1 pack of orange paper to make that minimum amount of cranes. Therefore, the solution is 6.
6.
Note: That's kinda a strange way of making cranes, using 2 pieces of paper.
