Answer:
321 closed boxes can be made.
Step-by-step explanation:
Given:- Rectangular metal sheet of 8.5m long (L)=850cm and 3.8m wide(W)=380cm.
Area of rectangular sheet = 


Area of rectangular metal sheet 
Now, to calculate total sheet required for 1 closed box of 
Area of sheet required for 1 closed box 



Area of sheet required for 1 closed box
Now,
Total number of boxes can be made = Area of rectangular sheet divided by Area of sheet required for 1 box

Total number of boxes can be made
Therefore 321 numbers of boxes can be made out of it.