Calculation of labour cost

Hi Manish!!! i have tried to solve your problem below.I hope it is right.       

Straight Piece Rate Method :                     No of Piece* rate per piece

                                                                                     = 150 * 3

                                                                              =450Rs

Differential Piece Rate Method:   Rate per unit    * No of :unit produced

                                                               = 3.60 (see W.N. 1) * 150

                                                               = 540Rs

working note 1: calculation of rate per piece

                            120% of piece rate if out put is above normal production

                           = 120% * 3 Rs ( As out put is 150 piece)

                           = 3.60Rs.

 Hasley Primeum Piece Rate Method :    Hours worked * rate per hour+50% (standard time-hours worked) * rate perhour                                            = 50 * 7.50Rs. + 50% (50-40) * 7.50 Rs.                                               =50*7.50+5*7.50 =375+37.50                                                  =412.50Rs.                             

       I hope my ans is right. please reply me wether its right or wrong.