Hatfield Corporation, which has only one product, has provided the following data concerning its most recent month of operations: $123 0 6,400 6,100 300 Selling price....... Units in beginning inventory... Units produced Units sold......... Units in ending inventory. Variable costs per unit: Direct materials Direct labor.... Variable manufacturing overhead .... Variable selling and administrative... Fixed costs: Fixed manufacturing overhead......... Fixed selling and administrative...... $45 $30 $1 $8 $140,800 $91,500 What is the net operating income for the month under variable costing? Select one: a. $6,600 b. $5,600 c. $(17,200) d. $12,200