A box filled with 12 honeydews has a mass of 17.07 kg. The same box when filled with 3 lemons has a mass of 0.87 kg. The mass of 1 honeydew is seven times the mass of 1 lemon. Find the mass of the box when it is empty. Express the answer in g.
1 kg = 1000 g

17.07 kg = 17070 g
0.87 kg = 870 g

1 lemon = 1 u
3 lemons = 3 x 1 u = 3 u

1 box + 3 lemons = 870
1 box + 3 u = 870 --- (1)

1 honeydew = 7 u
12 honeydews = 12 x 7 u = 84 u

1 box + 12 honeydews = 17070
1 box + 84 u = 17070 --- (2)

(2) - (1)
84 u - 3 u = 17070 - 870
81 u = 16200

1 u = 16200 ÷ 81 = 200

3 u = 3 x 200 = 600

From (1):
1 box + 3 u = 870
1 box + 600 = 870
 
1 box = 870 - 600 = 270

Mass of 1 box = 270 g

Answer(s): 270 g