Beechtree Corporation sells chewing gum and during January they ran production machines for 21,000 hours total and ncurred $13,000 in maintenance costs. During July they ran production machines for 10,000 hours total and incurred 57,200 in maintenance costs. Based on this data, what is the variable maintenance cost per machine hour? A. $0.55 per machine hour B. \$1.91 per machine hour C. $0.72 per machine hour D. $0.53 per machine hour