Map scales are supposed to be representative of what they portray, so when the scale of the map is 1cm/80 miles, that means that 1 cm measured on the map is equivalent to 80 miles in real life, and that 80 miles in real life will show up as 1 cm on the map.
So if two cities are 280 miles apart, that is (280/80) of 80 miles, which will be, on the map, (280/80) of 1 cm. So to get the distance on the map;
d = 1 x (280/80)
d = 3.5
So on the map, the cities are 3.5 cm apart
Hope this helped
