A box filled with 11 jackfruits has a mass of 6.41 kg. The same box when filled with 4 pomegranates has a mass of 0.81 kg. The mass of 1 jackfruit 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

6.41 kg = 6410 g
0.81 kg = 810 g

1 pomegranate = 1 u
4 pomegranates = 4 x 1 u = 4 u

1 box + 4 pomegranates = 810
1 box + 4 u = 810 --- (1)

1 jackfruit = 4 u
11 jackfruits = 11 x 4 u = 44 u

1 box + 11 jackfruits = 6410
1 box + 44 u = 6410 --- (2)

(2) - (1)
44 u - 4 u = 6410 - 810
40 u = 5600

1 u = 5600 ÷ 40 = 140

4 u = 4 x 140 = 560

From (1):
1 box + 4 u = 810
1 box + 560 = 810
 
1 box = 810 - 560 = 250

Mass of 1 box = 250 g

Answer(s): 250 g