What is the police force of counties on the east side?
select police_force from county_public_safety where location = "East"
What is the police force of counties on the west side?
select police_force from county_public_safety where location = "West"
What is the police force shared by county on both sides?
select police_force from county_public_safety where location = "East" intersect select police_force from county_public_safety where location = "West"
How many police officers are in the police force shared by county on both sides?
select count ( * ) from ( select police_force from county_public_safety where location = "East" intersect select police_force from county_public_safety where location = "West" )