Complete Question 
The complete question is shown on the first uploaded image 
Answer:
The concentration of  that should used originally is
 that should used originally is 
Explanation:
      From the question we are told that 
          The necessary elementary step is   
                   
           The  time taken for sixth of 0.5 M of reactant to react 
            The time available is 
              The desired concentration to  remain  
 
Let Z be the reactant ,   Y be the first product and X the second product
 Generally the elementary rate  law is mathematically as 
                     
Where k is the rate constant ,   is the concentration of Z
 is the concentration of Z
From the elementary rate law we see that the reaction is second order (This because the concentration of the reactant is raised to power 2 )
  For second  order reaction
             
Where  is the initial concentration of Z which a value of
 is the initial concentration of Z which a value of   
        From the question we are told that it take  9 hours  for the concentration of  the reactant to become 
                  
                   
                         
 
So      
                      
                           
                 =>    
   For   
                 
                 
                            
                             
                              