A22-in-long by 3.0-in-wide cast iron rectangular block is machined in a face milling operation using a 6.0-in-diameter cutter with 12 carbide inserts. the cutter path is centered over the width of the block. feed = 0.008 in/tooth and depth of cut = 0.60 in. at a cutting speed of 500 ft/min, the tool lasts for seven blocks. at a cutting speed of 250 ft/min, the tool lasts for 47 blocks. determine n and c in the taylor tool life equation. ignore the effect of the approach distance given by equation (21.18)