Rent'R Cars is a multisite car rental company in the city. It is trying out a new "return the car to the location most convenient for you" policy to improve customer service. But this means that the company has to constantly move cars around the city to maintain required levels of vehicle availability. The supply and demand for economy cars, and the total cost of moving these vehicles between sites, are shown below. What is the total cost? A$.\backslash (\backslash$$ $1,345\backslash )$ B$.\backslash (\backslash$$ $3,210\backslash )$ C$.\backslash (\backslash$$ $1,860\backslash )$ D$.\backslash (\backslash$$ $2\mathrm{.}600\backslash )$