The ratio of time of return stroke to time of forward stroke of a shaping machine is 0.6. The stroke is 250 mm and it makes 30 double strokes per minute. What is the overall average speed of operation?
(a) 3 – 75 n/min (b) 5 – 0 m/min (c) 7 – 5 m/min (d) 12 m/min