A spring of spring constant  5×103 N/m  &  stretched initially by 5 cm from the unstretched position.  Then work done required to stretch it further by another 5cm is

work done to stretch spring is W  =    12 K  (x22−x12) given spring constant is K=5 x103N/m; x2=10cm=10x10-2m;x1=5cm=5x10-2m W  =    12 ×5×103(102−52)×10−4 W  =    5×1032 ×0.0075 W  =    18.75 joule