Two identical tanks L and M contained some water. Tank L was ¹₄ filled and Tank M was ¹₅ filled. The ratio of the total mass of Tank L and the water in it to the total mass of Tank M and the water in it was 8 : 7. The total mass of the two tanks and the water they contained was 4050 g. What is the mass of an empty tank?
Mass of Tank L and the water inside = 8 u
Mass of Tank M and the water inside = 7 u

Total mass of the two tanks and the water inside them
= 8 u + 7 u
= 15 u

15 u = 4050

1 u = 4050 ÷ 15 = 270

Mass of Tank L and the water in it more than mass of Tank M and the water in it 
= 8 u - 7 u
= 1 u

Fraction of the water that Tank L had more than Tank M 
= ¹₄ - ¹₅
= ⁵₂₀ - ⁴₂₀
= ¹₂₀ 

¹₂₀ of the water capacity → 1 u
⁴₂₀ of the water capacity → 4 x 1 u = 4 u

Mass of an empty tank
= 7 u - 4 u
= 3 u
= 3 x 270
= 810 g

Answer(s): 810 g