A container filled with 14 mangoes has a mass of 13.72 kg. The same container when filled with 7 apples has a mass of 1.4 kg. The mass of 1 mango is six times the mass of 1 apple. Find the mass of the container when it is empty. Express the answer in g.
1 kg = 1000 g

13.72 kg = 13720 g
1.4 kg = 1400 g

1 apple = 1 u
7 apples = 7 x 1 u = 7 u

1 container + 7 apples = 1400
1 container + 7 u = 1400 --- (1)

1 mango = 6 u
14 mangoes = 14 x 6 u = 84 u

1 container + 14 mangoes = 13720
1 container + 84 u = 13720 --- (2)

(2) - (1)
84 u - 7 u = 13720 - 1400
77 u = 12320

1 u = 12320 ÷ 77 = 160

7 u = 7 x 160 = 1120

From (1):
1 container + 7 u = 1400
1 container + 1120 = 1400
 
1 container = 1400 - 1120 = 280

Mass of 1 container = 280 g

Answer(s): 280 g