What is the safest way to dispose of old bank account statements?

The owner of firewood to go is considering buying a hydraulic wood splitter which sells for $50,000. he figures it will cost an additional $100 per cord to purchase and split wood with this machine, while he can sell each cord of split wood for $125. if, for this machine, design capacity is 50 cords per day, effective capacity is 40 cords per day, and actual output is expected to be 32 cords per day, what would be its efficiency?