1. Joey corp., a retailer, plans to sell 28,000 units of its product called "hot sandwiches" during the month of October. If joey has 6000 units on hand tr the start of the month, and plants to have 9000 units on hand at the end of the month, how many units of "hot sandwiches" must be purchased from the supplier during the month?

A. 28,000

B. 25,000

C. 37,000

D. 31,000