A schematic diagram of peripheral milling is shown in the Figure.

If $$t$$ is the depth of cut and $$d$$ is the diameter of the milling cutter, then the length of approach $$\left( {la} \right)$$ is expressed as

In drilling operation, a twist-drill of $$30$$ $$mm$$ diameter with point angle of $$118$$ degrees is used. If the $$CNC$$ command issued to execute the drilling operation is $$G90$$ $$G01$$ $$Z??$$ $$F20.$$ The datum is defined on the top surface of the work material and the approach distance is $$3$$ $$mm.$$ Then, to achieve a cylindrical hole depth of $$40$$ $$mm,$$ the $$Z$$ coordinate to be provided in the $$CNC$$ command, in $$mm,$$ is ______________.

In a slab milling operation, a cutter of $$75$$ $$mm$$ diameter with sufficient width is used to remove $$5$$ $$mm$$ thick material from a $$200$$ $$mm$$ long part in a single pass. The minimum length of travel, in $$mm,$$ for the cutter to engage and completely cut the part surface is ______________.

An $$HSS$$ drill of $$20mm$$ diameter with $$5mm$$ cone height is used to drill a through hole in a steel work-piece of $$50mm$$ thickness. Cutting speed of $$10m/min$$ and feed rate of $$0.3mm/rev$$ are used. The drilling time, in seconds, neglecting the approach and over travel, is ______________