Suppose you have two locations (Stations A and B) that are 200 km apart from each other. Station A is reporting a surface air pressure of 1020 mb while Station B is reporting a surface air pressure of 1012 mb. The pressure gradient between the two cities would be:
a. 200mb/8km
b. 8mb/200km
c. 50mb/4km
d. 4mb/50km