Answer:
The width of the sheet is   
Explanation:
   From the question we are told that 
              The distance of point P above a  large sheet of metal is 
              The current on the large metal sheet  is  
               The  distance of the the point P below a long wire 
                The current on the long wire is  
                 The magnetic field at  P is  
Generally magnetic field  of P long wire is mathematically represented as
                 
Generally magnetic field  of P large sheet of meta is mathematically represented as
               
Where K is the current per unit width 
  The total magnetic field at P is 
                   
Making K the subject of formula 
                  
  Substituting values
                    
                         
Generally K is mathematically represented as
                 
Where w is the width of the large sheet 
Therefore the width  of the metal sheet   
                                                                          
                                                                          