The formula with 4.8 substituted
miles = 4.8 ÷ 1.609344 = 2.983
The constant is an exact definition, not a rounded factor: the mile is 1.609344 km, the US gallon is 3.785411784 litres and the imperial gallon is 4.54609 litres. The Kilometres to Miles Converter explains where each comes from and gives a longer table.
At a walking pace of 5 km/h, 4.8 km takes about 58 minutes. At an easy running pace of 10 km/h it takes about 29. In metres it is 4,800.
What 4.8 kilometres means in practice
4.8 km is the three mile mark, near enough: three miles is 4.828 km. Twelve laps of a track. It is a common school cross-country distance and a standard route length for beginner running plans.