A container filled with 9 durians has a mass of 9 kg. The same container when filled with 4 pomegranates has a mass of 0.74 kg. The mass of 1 durian is seven times the mass of 1 pomegranate. Find the mass of the container when it is empty. Express the answer in g.
1 kg = 1000 g

9 kg = 9000 g
0.74 kg = 740 g

1 pomegranate = 1 u
4 pomegranates = 4 x 1 u = 4 u

1 container + 4 pomegranates = 740
1 container + 4 u = 740 --- (1)

1 durian = 7 u
9 durians = 9 x 7 u = 63 u

1 container + 9 durians = 9000
1 container + 63 u = 9000 --- (2)

(2) - (1)
63 u - 4 u = 9000 - 740
59 u = 8260

1 u = 8260 ÷ 59 = 140

4 u = 4 x 140 = 560

From (1):
1 container + 4 u = 740
1 container + 560 = 740
 
1 container = 740 - 560 = 180

Mass of 1 container = 180 g

Answer(s): 180 g