A box filled with 11 mangoes has a mass of 13.38 kg. The same box when filled with 6 starfruits has a mass of 1.38 kg. The mass of 1 mango is six times the mass of 1 starfruit. Find the mass of the box when it is empty. Express the answer in g.
1 kg = 1000 g

13.38 kg = 13380 g
1.38 kg = 1380 g

1 starfruit = 1 u
6 starfruits = 6 x 1 u = 6 u

1 box + 6 starfruits = 1380
1 box + 6 u = 1380 --- (1)

1 mango = 6 u
11 mangoes = 11 x 6 u = 66 u

1 box + 11 mangoes = 13380
1 box + 66 u = 13380 --- (2)

(2) - (1)
66 u - 6 u = 13380 - 1380
60 u = 12000

1 u = 12000 ÷ 60 = 200

6 u = 6 x 200 = 1200

From (1):
1 box + 6 u = 1380
1 box + 1200 = 1380
 
1 box = 1380 - 1200 = 180

Mass of 1 box = 180 g

Answer(s): 180 g