A container filled with 13 durians has a mass of 17.51 kg. The same container when filled with 5 lemons has a mass of 1.17 kg. The mass of 1 durian is seven times the mass of 1 lemon. Find the mass of the container when it is empty. Express the answer in g.
1 kg = 1000 g

17.51 kg = 17510 g
1.17 kg = 1170 g

1 lemon = 1 u
5 lemons = 5 x 1 u = 5 u

1 container + 5 lemons = 1170
1 container + 5 u = 1170 --- (1)

1 durian = 7 u
13 durians = 13 x 7 u = 91 u

1 container + 13 durians = 17510
1 container + 91 u = 17510 --- (2)

(2) - (1)
91 u - 5 u = 17510 - 1170
86 u = 16340

1 u = 16340 ÷ 86 = 190

5 u = 5 x 190 = 950

From (1):
1 container + 5 u = 1170
1 container + 950 = 1170
 
1 container = 1170 - 950 = 220

Mass of 1 container = 220 g

Answer(s): 220 g