Answer:
The correct options are 1 and 3.
Step-by-step explanation:
It is given that x represents the number of small boxes and y represents the number of large boxes.
The post office has 10 small boxes and 9 large boxes in stock.
He needs at least 4 small boxes.
He will buy no more than 15 boxes.
Therefore options 1 and 3 are correct.
Therefore options 2 and 4 are incorrect.