Kiona, was there another symbol with the 6kg, such as m (meters) and s (seconds)?  one N (Newton) = 1 kilogram times 1 meter per second squared:  1 N = 1 kg·m/s², so if we have 6 kg·m/s², then we'd have 6 kg·m/s2 + 4 kg·m/s2 = 10 kg·m/s2, or 10 Newtons, or 10N