A container filled with 13 king melons has a mass of 12.69 kg. The same container when filled with 9 pomegranates has a mass of 1.29 kg. The mass of 1 king melon is eight times the mass of 1 pomegranate. Find the mass of the container when it is empty. Express the answer in g.
1 kg = 1000 g

12.69 kg = 12690 g
1.29 kg = 1290 g

1 pomegranate = 1 u
9 pomegranates = 9 x 1 u = 9 u

1 container + 9 pomegranates = 1290
1 container + 9 u = 1290 --- (1)

1 king melon = 8 u
13 king melons = 13 x 8 u = 104 u

1 container + 13 king melons = 12690
1 container + 104 u = 12690 --- (2)

(2) - (1)
104 u - 9 u = 12690 - 1290
95 u = 11400

1 u = 11400 ÷ 95 = 120

9 u = 9 x 120 = 1080

From (1):
1 container + 9 u = 1290
1 container + 1080 = 1290
 
1 container = 1290 - 1080 = 210

Mass of 1 container = 210 g

Answer(s): 210 g