A container filled with 13 king melons has a mass of 7.45 kg. The same container when filled with 3 apples has a mass of 0.59 kg. The mass of 1 king melon is four times the mass of 1 apple. Find the mass of the container when it is empty. Express the answer in g.
1 kg = 1000 g

7.45 kg = 7450 g
0.59 kg = 590 g

1 apple = 1 u
3 apples = 3 x 1 u = 3 u

1 container + 3 apples = 590
1 container + 3 u = 590 --- (1)

1 king melon = 4 u
13 king melons = 13 x 4 u = 52 u

1 container + 13 king melons = 7450
1 container + 52 u = 7450 --- (2)

(2) - (1)
52 u - 3 u = 7450 - 590
49 u = 6860

1 u = 6860 ÷ 49 = 140

3 u = 3 x 140 = 420

From (1):
1 container + 3 u = 590
1 container + 420 = 590
 
1 container = 590 - 420 = 170

Mass of 1 container = 170 g

Answer(s): 170 g