The answer is 81.6 km.
This is simple proportion. If 1 cm on the map is 12 km of the actual distance, then 6.8 cm on the map are how many km of the actual distance:
[tex] \frac{1cm}{12km}= \frac{6.8cm}{x} \\ x*1cm = 12km * 6.8cm \\ x = \frac{12km * 6.8 cm}{1cm} \\ x = 81.6 km[/tex]
Therefore, on the map with scale 1 cm : 12 km, if the distance on the map is 6.8 cm, then the actual distance between the cities is 81.6 km
