Betty DeRose, Inc. reported the following cost data for May: Direct labor Applied overhead Actual overhead Direct materials purchased Total manufacturing costs $33,680 $19,320 $20,070 $22,840 $80,410 Betty DeRose, Inc. reported the following inventory balances during May: Direct materials Work in process Finished goods May 1 ? $24,000 $66,000 May 31 ? $37,000 $42,000 The ending direct material inventory is 60% of the amount of the beginning direct material inventory. Calculate Betty DeRose's direct material inventory balance at May 31