In September, Smith Company had the following financial statement amounts related to producing 500 units: ...... Direct materials......................... ...... $27,000 ...... Depreciation expense................ ........ 11,000 ...... Sales revenue............................ ........ 95,000 ...... Direct labour............................. ........ 23,000 ...... Rent expense............................ ........ 25,000 How much is total contribution margin for September? a. $9,000 b. $45,000 c. $68,000 d. $20,000