Let us find the area for 830 bricks
 14  ft 9 in   =14. 75 ft
 So  14.75  *  6  =   88.5 sq ft
  
 The required wall square footage  = 
 36 ft 6 in  = 36.5 ft  * 6ft   =  219 sq ft
  
 So...the number of bricks required for the new wall can be found by a proportion
  
 N / 219  = 830  / 88.5   multiply both sides by 219 
  
 N =  219 * 830 / 88.5   ≈  2054 bricks    
  
 It will take
  
 [2054/ 300 ] hrs to construct  the wall
  
 And the hourly rate  is  4000/8  = $500
  
 So...the total cost   ≈  [2054/ 300] * 500   = $ 3423.16
  
 The third answer  seems the closest   [the difference is due to rounding by me ]
  
  
  
  
 