None.
140 kilometres is a measure of distance. It could take seconds to travel that distance or years. MPH (or miles per hour) is a measure of speed. The two measure different things and conversion from one to the other is not valid.
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6 mph = 9.6561 km/h
400 km in what time is missing
429.7 km/h
km is a measurement of distance and mph is a measure of velocity. However 1 mph =1.609344 kph (km per hour) so 400 mph = 400 * 1.609344 = 643.7376 kph
432