A box filled with 11 watermelons has a mass of 16.88 kg. The same box when filled with 5 passion fruits has a mass of 1.11 kg. The mass of 1 watermelon is eight times the mass of 1 passion fruit. Find the mass of the box when it is empty. Express the answer in g.
1 kg = 1000 g

16.88 kg = 16880 g
1.11 kg = 1110 g

1 passion fruit = 1 u
5 passion fruits = 5 x 1 u = 5 u

1 box + 5 passion fruits = 1110
1 box + 5 u = 1110 --- (1)

1 watermelon = 8 u
11 watermelons = 11 x 8 u = 88 u

1 box + 11 watermelons = 16880
1 box + 88 u = 16880 --- (2)

(2) - (1)
88 u - 5 u = 16880 - 1110
83 u = 15770

1 u = 15770 ÷ 83 = 190

5 u = 5 x 190 = 950

From (1):
1 box + 5 u = 1110
1 box + 950 = 1110
 
1 box = 1110 - 950 = 160

Mass of 1 box = 160 g

Answer(s): 160 g