A small petroleum company owns two refineries. Refinery 1 costs $20,000 per day to. Operate, and it can produce 400 barrels of high-grade oil, 300 barrels of medium-grade oil, and 200 barrels of low-grade oil each day. Refinery 2 is newer and more modern. It costs $25,000 per day to operate, and it can produce 300 barrels of high-grade oil, 400 barrels of medium-grade oil, and 500 barrels of low-grade oil each day.

The company has orders totaling 25,000 barrels of high-grade oil, 27,000 barrels of medium-grade oil, and 30,000 barrels of low-grade oil. Use the simplex method to determine how many days should it run each refinery to minimize its costs and still refine enough oil to meet its orders? Determine the value of the objective function, and the slack/surplus variables, as well as identify the binding/non-binding constraints.