9. A store needed to receive 185 kg of candies in closed boxes from the warehouse. The warehouse has boxes of candies weighing 16 kg, 17 kg, and 21 kg. What boxes and how many could the store receive?
9. We notice that $185=37 \cdot 5$ and $16+21=37$. Therefore, the store could have received 5 boxes weighing 21 kg each and 5 boxes weighing 16 kg each. Since the number 185 has been factored into prime factors, the problem has a unique solution.