A box filled with 13 mangoes has a mass of 16.88 kg. The same box when filled with 3 pomegranates has a mass of 0.72 kg. The mass of 1 mango is eight 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

16.88 kg = 16880 g
0.72 kg = 720 g

1 pomegranate = 1 u
3 pomegranates = 3 x 1 u = 3 u

1 box + 3 pomegranates = 720
1 box + 3 u = 720 --- (1)

1 mango = 8 u
13 mangoes = 13 x 8 u = 104 u

1 box + 13 mangoes = 16880
1 box + 104 u = 16880 --- (2)

(2) - (1)
104 u - 3 u = 16880 - 720
101 u = 16160

1 u = 16160 ÷ 101 = 160

3 u = 3 x 160 = 480

From (1):
1 box + 3 u = 720
1 box + 480 = 720
 
1 box = 720 - 480 = 240

Mass of 1 box = 240 g

Answer(s): 240 g