This question was well understood and also well attempted by most candidates as they were able to use the relation w = ½ ke2 correctly.  However, very few use wrong formula.  That is w = ½ ke and arithmetic blunder thus  = 55.06 – 55 = 0.6.Instead of 0.06          
The expected solution is
Work done      =          ½ Ke2                                                                                     
                        =          ½ x 700 x (55.06 – 55)2                                                         
                        =          1.26 J