An emergency repair and service company serves its customers which are located in four different industrial estates.
Estate A is located at grid reference (5, 7) and has 15 customers.
Estate B is located at grid reference (6, 3) and has 20 customers.
Estate C is located at grid reference (10, 2), has 15 customers and is twice as likely to require service, than the company's other customers.
Estate D is located at grid reference (12, 3) and has 10 customers. At what grid reference should the company locate its service centre?