Linear Programming Problem

Okay, I am not feeling really well, and this is frustrating me quite a bit. :mad:

Here is the problem:

A manufacturer of refrigerators must ship at least 100 refrigerators to its two West Coast warehouses. Warehouse A holds a maximum of 75 refrigerators and Warehous B holds a maximum of 80 refrigerators. It costs $12 to ship a refrigerator to warehouse A and $10 to ship one to warehouse B. Union rules require that at least 300 workers be hired. Shipping a refrigerator to Warehouse A requires 4 workers, while shipping a refrigerator to Warehouse B requires 2 workers. How many refrigerators should be shipped to each warehouse to minimize costs? What is the minimum cost?

Okay, now here is my problem: Teacher says that there are three constraints and then the objective function. So, I have:

Objective function: c=12x+10y

Constraints: 1. 75x+80y >/= 100

2. 4x + 2y >/= 300

Now, could someone give me a hint as to what I am looking for in the third constraint? I mean I have a constraint for space and workers, what else is there? I have a feeling I am missing something obvious.