An industrial engineer is trying to study the relationship between the average stock in the warehouse and the total inventory cost. /she collected the following data:

Month	Average stock level (units)	Total warehouse cost ($)
June	19500	44000
July	21000	46300
August	18500	42000
September	16200	39430

1. Using the high-low method, estimate a cost formula between the average stock level and the total warehouse cost.
2. Estimate the cost during October if the average stock of the last year was 13500 units.
3. If at October this year, the total warehouse cost was equal to 26,650. What would have the average stock level inventory been?