A fire hydrant with a blue cap provides water at a rate of 1500 gallons per minute. A fire hydrant with a green cap provides water at a rate of 1000 gallons per minute. A fire hydrant with a purple cap provides water at half the rate of a fire hydrant with a green cap.
Write an equation to relate the flow of water from the blue hydrant, b, to the flow from the green hydrant, g.