A CNC worktable is driven by a closed loop control system consisting of a drive unit (stepper motor), lead screw, and optical encoder. The stepper motor which is driven by voltage pulse from pulse generator exicutes 1 step/pulse. The frequency of the pulse generator is 140 pulse/s. The stepper  motor rotates 210 steps per revolution drives the table through a gear box  and a lead screw nut mechanism. The gear ratio as 1/2 ( Output speed to input speed) and the lead screw has a pitch of 6 mm. The table speed will be ________ mm/min.