Song, Inc., uses the high-low method to analyze cost behavior. The company observed that at 22,000 machine hours of activity, total maintenance costs averaged $33.40 per hour. When activity jumped to 25,000 machine hours, which was still within the relevant range, the average total cost per machine hour was $30.40. On the basis of this information, the variable cost per machine hour was: O $8.40 O $22.00 O $25,00 O $30.40 $32 10