A container filled with 12 mangoes has a mass of 13.96 kg. The same container when filled with 7 kiwis has a mass of 1.61 kg. The mass of 1 mango is six times the mass of 1 kiwi. Find the mass of the container when it is empty. Express the answer in g.
1 kg = 1000 g

13.96 kg = 13960 g
1.61 kg = 1610 g

1 kiwi = 1 u
7 kiwis = 7 x 1 u = 7 u

1 container + 7 kiwis = 1610
1 container + 7 u = 1610 --- (1)

1 mango = 6 u
12 mangoes = 12 x 6 u = 72 u

1 container + 12 mangoes = 13960
1 container + 72 u = 13960 --- (2)

(2) - (1)
72 u - 7 u = 13960 - 1610
65 u = 12350

1 u = 12350 ÷ 65 = 190

7 u = 7 x 190 = 1330

From (1):
1 container + 7 u = 1610
1 container + 1330 = 1610
 
1 container = 1610 - 1330 = 280

Mass of 1 container = 280 g

Answer(s): 280 g