If x represents the mass of 1 ball in kg, then the balance shows ...
... 6x = x + 9 kg
... 5x = 9 kg
Then 6x is ...
... (6/5)·5x = (6/5)·9 kg = 10.8 kg
0.8 kg = 0.8·1000 g = 800 g
so 10.8 kg is ...
... D. 10 kg 800 g
