Box T and Box U are identical. ⁵₆ of Box T and ³₅ of Box U are filled with sand. The mass of Box U with its contents is ⁹₁₀ the mass of Box T with its contents. The total mass of the two boxes with their contents is 266 kg. Find the mass of an empty box.
Mass of Box T and its contents = 10 u
Mass of Box U and its contents = 9 u

Total mass of the two boxes with their contents
= 10 u + 9 u
= 19 u

19 u = 266 

1 u = 266 ÷ 19 = 14

Mass of Box T with its concents more than mass of Box U with its contents
= 10 u - 9 u
= 1 u
= 1 x 14
= 14 kg

Fraction of the sand that Box T had more than Box U
= ⁵₆ - ³₅
= ²⁵₃₀ - ¹⁸₃₀
= ⁷₃₀

⁷₃₀ of the capacity of sand in a box → 14
¹₃₀ of the capacity of sand in a box → 14 ÷ 7 = 2
¹⁸₃₀ of the capacity of sand in a box → 18 x 2 = 36 

Mass of the sand and Box U
= 9 u
= 9 x 14
= 126 kg

Mass of the empty box
= 126 - 36
= 90 kg

Answer(s): 90 kg