Answer:
Scale 1:500 000 means, that 1 centimeter in map, is 500 000 centimeters in real life.
1. Change 500 000 into meters/kilometers:
500 000 cm = 5 000 m = 5 km
2. Multiply length between cities by score of operation above to get the answer:
5 * 7 = 35
So distance between cities is 35 kilometers