Complete Question 
The complete question is shown on the first uploaded image 
Answer:
The acceleration would be   
     
Explanation:
The objective of this solution is to obtain the acceleration of the particle 
        Now looking at Newton law which is mathematically represented as
                        
   Where F is the force experience by a particle 
               m is the mass of the particle 
               a is the acceleration of the particle 
   And also this force is equivalent to magnetic force in a magnetic field which is mathematically represented as
                     
 Where q is the charge of the particle 
              v is the velocity of the  charge 
              B is the magnetic field the charge is under it influence 
   Now equating this two formulas 
                    
  Making a the subject we have 
                   
In the question the direction of the is in the positive x-axis which is  hence the direction would be in the
 hence the direction would be in the  direction
 direction
       So substituting   for B
 for B
                     
       Substituting        for v  and
  for v  and  for q
 for q 
                      
                        
                       
According to vector multiplication
                                              
      So 
                