What is the distance in km between two cites that are 7.5 cm apart on a 1:24 000 scale

The scale 1:24000 means that 1 unit on the map represents 24000 of that unit on the ground.

7.5 cm on the map represents 7.5 x 24000 = 180000 cm on the ground.

180000 cm = 1800 m (dividing by 100 cm per m)

1800 m = 1.8 km (dividing by 1000 m per km)

Those "cities" are really close together!