A container filled with 9 watermelons has a mass of 6.77 kg. The same container when filled with 3 kiwis has a mass of 0.65 kg. The mass of 1 watermelon 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

6.77 kg = 6770 g
0.65 kg = 650 g

1 kiwi = 1 u
3 kiwis = 3 x 1 u = 3 u

1 container + 3 kiwis = 650
1 container + 3 u = 650 --- (1)

1 watermelon = 6 u
9 watermelons = 9 x 6 u = 54 u

1 container + 9 watermelons = 6770
1 container + 54 u = 6770 --- (2)

(2) - (1)
54 u - 3 u = 6770 - 650
51 u = 6120

1 u = 6120 ÷ 51 = 120

3 u = 3 x 120 = 360

From (1):
1 container + 3 u = 650
1 container + 360 = 650
 
1 container = 650 - 360 = 290

Mass of 1 container = 290 g

Answer(s): 290 g