For this problem you have a function, in the form of equation, that relates the actual distance and the distance of the points in the map.
The function is, y = 8x where x is distance i n cm, in the map, and y is actual distance in Km
Then, given that you know the actual distance is y = 64 km, you can solve for x:
y = 8x => x = y/8 = 64/8 = 8
Answer: distance in the map is 8 cm