Two identical tanks W and X contained some water. Tank W was ¹₂ filled and Tank X was ¹₃ filled. The ratio of the total mass of Tank W and the water in it to the total mass of Tank X and the water in it was 5 : 4. The total mass of the two tanks and the water they contained was 2160 g. What is the mass of an empty tank?
Mass of Tank W and the water inside = 5 u
Mass of Tank X and the water inside = 4 u

Total mass of the two tanks and the water inside them
= 5 u + 4 u
= 9 u

9 u = 2160

1 u = 2160 ÷ 9 = 240

Mass of Tank W and the water in it more than mass of Tank X and the water in it 
= 5 u - 4 u
= 1 u

Fraction of the water that Tank W had more than Tank X 
= ¹₂ - ¹₃
= ³₆ - ²₆
= ¹₆ 

¹₆ of the water capacity → 1 u
²₆ of the water capacity → 2 x 1 u = 2 u

Mass of an empty tank
= 4 u - 2 u
= 2 u
= 2 x 240
= 480 g

Answer(s): 480 g