Scale of map = 1:80000000
This means 1 unit on map shows 80000000 units on the real world.
If A and B are 3cm apart on map,
actual distance = 3cm×800000000 = 240000000 cm = 2400 km
If C and D are at a distance 3200km apart,
3200km = 3200×1000×100 cm = 320000000cm
on the map, it should be = 320000000/80000000 = 4cm
So distance on map is 4cm.