The formula with 7 substituted
miles = 7 ÷ 1.609344 = 4.350
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, 7 km takes about 84 minutes. At an easy running pace of 10 km/h it takes about 42. In metres it is 7,000.
What 7 kilometres means in practice
7 km is 4.35 miles, a bit over the length of the popular running circuit round Central Park's reservoir and drives, and about 40 minutes at an easy running pace.