A box filled with 11 watermelons has a mass of 6.76 kg. The same box when filled with 8 chikoos has a mass of 1.36 kg. The mass of 1 watermelon is four times the mass of 1 chikoo. Find the mass of the box when it is empty. Express the answer in g.
1 kg = 1000 g

6.76 kg = 6760 g
1.36 kg = 1360 g

1 chikoo = 1 u
8 chikoos = 8 x 1 u = 8 u

1 box + 8 chikoos = 1360
1 box + 8 u = 1360 --- (1)

1 watermelon = 4 u
11 watermelons = 11 x 4 u = 44 u

1 box + 11 watermelons = 6760
1 box + 44 u = 6760 --- (2)

(2) - (1)
44 u - 8 u = 6760 - 1360
36 u = 5400

1 u = 5400 ÷ 36 = 150

8 u = 8 x 150 = 1200

From (1):
1 box + 8 u = 1360
1 box + 1200 = 1360
 
1 box = 1360 - 1200 = 160

Mass of 1 box = 160 g

Answer(s): 160 g