Box K and Box L are identical. ⁵₆ of Box K and ³₈ of Box L are filled with sand. The mass of Box L with its contents is ⁸₉ the mass of Box K with its contents. The total mass of the two boxes with their contents is 187 kg. Find the mass of an empty box.
Mass of Box K and its contents = 9 u
Mass of Box L and its contents = 8 u

Total mass of the two boxes with their contents
= 9 u + 8 u
= 17 u

17 u = 187 

1 u = 187 ÷ 17 = 11

Mass of Box K with its concents more than mass of Box L with its contents
= 9 u - 8 u
= 1 u
= 1 x 11
= 11 kg

Fraction of the sand that Box K had more than Box L
= ⁵₆ - ³₈
= ²⁰₂₄ - ⁹₂₄
= ¹¹₂₄

¹¹₂₄ of the capacity of sand in a box → 11
¹₂₄ of the capacity of sand in a box → 11 ÷ 11 = 1
⁹₂₄ of the capacity of sand in a box → 9 x 1 = 9 

Mass of the sand and Box L
= 8 u
= 8 x 11
= 88 kg

Mass of the empty box
= 88 - 9
= 79 kg

Answer(s): 79 kg