A box filled with 8 king melons has a mass of 3.69 kg. The same box when filled with 7 pomegranates has a mass of 0.94 kg. The mass of 1 king melon is four times the mass of 1 pomegranate. Find the mass of the box when it is empty. Express the answer in g.
1 kg = 1000 g

3.69 kg = 3690 g
0.94 kg = 940 g

1 pomegranate = 1 u
7 pomegranates = 7 x 1 u = 7 u

1 box + 7 pomegranates = 940
1 box + 7 u = 940 --- (1)

1 king melon = 4 u
8 king melons = 8 x 4 u = 32 u

1 box + 8 king melons = 3690
1 box + 32 u = 3690 --- (2)

(2) - (1)
32 u - 7 u = 3690 - 940
25 u = 2750

1 u = 2750 ÷ 25 = 110

7 u = 7 x 110 = 770

From (1):
1 box + 7 u = 940
1 box + 770 = 940
 
1 box = 940 - 770 = 170

Mass of 1 box = 170 g

Answer(s): 170 g