We are given that:
3/10 in = 7/8 mi
Use cross multiplication to get the scale as follows:
3/10 in = 7/8 mi
3(8) in = 7(10) mi
24 in = 70 mi
24/70 in = 1 mi
1 mi = 0.3429 in
Therefore:
unit rate of the map is: 1 mi = 0.3429 in
This means that:
each one 1 mile in reality is represented by 0.3429 inches on the map