A firm produces wooden packing boxes to be used in the local seafood industry. Previous operations allowed the company to make 600 boxes per day, using 45 labour hours. The company has introduced some small changes in equipment, and conducted appropriate job training, so that production levels have risen to 670 boxes per day. These changes did not require any change in the amount of capital spending or labour use. What is the firm's new labour productivity (in boxes/hour)?