A box filled with 15 jackfruits has a mass of 13.7 kg. The same box when filled with 8 persimmons has a mass of 1.64 kg. The mass of 1 jackfruit is five times the mass of 1 persimmon. Find the mass of the box when it is empty. Express the answer in g.
1 kg = 1000 g

13.7 kg = 13700 g
1.64 kg = 1640 g

1 persimmon = 1 u
8 persimmons = 8 x 1 u = 8 u

1 box + 8 persimmons = 1640
1 box + 8 u = 1640 --- (1)

1 jackfruit = 5 u
15 jackfruits = 15 x 5 u = 75 u

1 box + 15 jackfruits = 13700
1 box + 75 u = 13700 --- (2)

(2) - (1)
75 u - 8 u = 13700 - 1640
67 u = 12060

1 u = 12060 ÷ 67 = 180

8 u = 8 x 180 = 1440

From (1):
1 box + 8 u = 1640
1 box + 1440 = 1640
 
1 box = 1640 - 1440 = 200

Mass of 1 box = 200 g

Answer(s): 200 g