Help solving please

ssignment i Saved A system consists of three particles with these masses and velocities: mass 3.00 kg, moving north at 3.00 m/s; mass 4.00 kg, moving south at 3.50 m/s; and mass(7.00 kg, moving north at 2.00 m/s. What is the total momentum of the system? Take north as the positive axis. Enter a positive answer if the total momentum is due north and a negative answer if the total momentum is due south. kg . m/s