Answer:
8.929kg
Explanation:
The work done to place the box at tree house=350 J.
The distance from ground to tree house =4.0 m and [tex]g=9.8m/s^2[/tex]
[tex]E=mgh\\\\m=350J/(9.8m/s^2\times 4.0m)\\\\m=8.929kg[/tex]
Hence the mass of the box is 8.929kg