The top layer of a flat 750 mm × 300 mm rectangular mild steel plate is to be machined with a single depth of cut using a shaping machine. The plate has been fixed by keeping 750 mm side along the tool travel direction. If the approach and the over-travel are 25 mm each, the average cutting speed is 10 m/min, the feed rate is 0.4 mm/stroke, and the ratio of return time to cutting time of the tool is 1 : 2, the time (in minutes) required to complete the machining operation is _______. [round off to one decimal place]