The length, width and thickness of a steel sample are $400$ mm, $40$ mm and $20$ mm, respectively. Its thickness needs to be uniformly reduced by $2$ mm in a single pass by using horizontal slab milling. The milling cutter (diameter: $100$ mm, width: $50$ mm) has $20$ teeth and rotates at $1200$ rpm. The feed per tooth is $0.05$ mm. The feed direction is along the length of the sample. If the over-travel distance is the same as the approach distance and time taken to complete the required machining task are
1. $14$ mm, $18.4$ s
2. $21$ mm, $28.9$ s
3. $21$ mm, $39.4$ s
4. $14$ mm, $21.4$ s