Box F and Box G are identical. ³₄ of Box F and ²₇ of Box G are filled with sand. The mass of Box G with its contents is ⁷₉ the mass of Box F with its contents. The total mass of the two boxes with their contents is 208 kg. Find the mass of an empty box.
Mass of Box F and its contents = 9 u
Mass of Box G and its contents = 7 u

Total mass of the two boxes with their contents
= 9 u + 7 u
= 16 u

16 u = 208 

1 u = 208 ÷ 16 = 13

Mass of Box F with its concents more than mass of Box G with its contents
= 9 u - 7 u
= 2 u
= 2 x 13
= 26 kg

Fraction of the sand that Box F had more than Box G
= ³₄ - ²₇
= ²¹₂₈ - ⁸₂₈
= ¹³₂₈

¹³₂₈ of the capacity of sand in a box → 26
¹₂₈ of the capacity of sand in a box → 26 ÷ 13 = 2
⁸₂₈ of the capacity of sand in a box → 8 x 2 = 16 

Mass of the sand and Box G
= 7 u
= 7 x 13
= 91 kg

Mass of the empty box
= 91 - 16
= 75 kg

Answer(s): 75 kg