What is the drilling time for producing a hole in an MS sheet of 25mm thickness using an HSS drill of 20mm diameter? The cutting speed and feed for drill 20m/min and 0.25mm/revolution respectively. Neglect time taken for setting up, approaching and travelling of tools.
(a) 0.314 min (b) 0.236 min
(c) 0.438 min (d) 0.443 min