Kilometers (km) are used as a unit of distance in the majority of countries worldwide, including Europe but excluding the United States. The conversion of the distance to the time (in hours) is the very common task, since it allows you to estimate travel time. You need to know a speed, for example average of speed your car in the trip, to make that conversion.

Multiply the distance, if given in miles, by the factor 1.609 to compute it in kilometers. For example, 86 miles would be converted to 86 x 1.609 or 138.374 kilometers.

Convert the speed into the kilometers per hour unit. If the speed is given in miles per hour multiply it by 1.609. If the speed is measured in meters per second (m/s), multiply it by 3.6. For example, the speed of 15 m/s corresponds to 15 x 3.6 or 54 km/h.

Divide distance (in km) by the speed (in km/h) to calculate the time (in hours). In our example, time is 138.374 km/ 54 km/h = 2.562 hours.

Multiply the decimal portion of the number of hours by "60" to convert it to minutes. In our example, the decimal part 0.562; 0.562 x 60 = 33.72 min that can be rounded to 34 minutes. Thus 2.562 h corresponds to 2 h 34 min.
References
 CIA.gov: World Fact Book (Appendix G)
 Physics;” John D. Cutnell and Kenneth W. Johnson; 2006
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