A container filled with 15 durians has a mass of 20.19 kg. The same container when filled with 6 passion fruits has a mass of 1.38 kg. The mass of 1 durian is seven times the mass of 1 passion fruit. Find the mass of the container when it is empty. Express the answer in g.
1 kg = 1000 g

20.19 kg = 20190 g
1.38 kg = 1380 g

1 passion fruit = 1 u
6 passion fruits = 6 x 1 u = 6 u

1 container + 6 passion fruits = 1380
1 container + 6 u = 1380 --- (1)

1 durian = 7 u
15 durians = 15 x 7 u = 105 u

1 container + 15 durians = 20190
1 container + 105 u = 20190 --- (2)

(2) - (1)
105 u - 6 u = 20190 - 1380
99 u = 18810

1 u = 18810 ÷ 99 = 190

6 u = 6 x 190 = 1140

From (1):
1 container + 6 u = 1380
1 container + 1140 = 1380
 
1 container = 1380 - 1140 = 240

Mass of 1 container = 240 g

Answer(s): 240 g