Each lap around the track is 400 m.
Therefore, if someone run 2 laps, we have,
[tex]400\times2=800m[/tex]Similarly, when someone runs 5 laps, we have,
[tex]400m\times5=2000m[/tex]Therefore when someone runs x laps,
[tex]400m\times x=400x\text{ m}[/tex]When x= 1,
[tex]400m\times1=400m[/tex]