(a)
Apply Newton's second law of motion, Net force is,
             Â
ΣF = F cos17.6 - f = 0
               F
cos17.6 - f = 0
                      Â
     F  = f / cos17.6
=42.4/0.9532
                Â
   Fshopper= 44.48 N
(b)
Work done by the pushing force is,
W1 = Fd cos17.6
                Â
= (42.4)(17.6)( cos17.6 )
 Â
              Â
≈ 711 J
(c)
Work done by frictional force is,
W = fd Cos180
           Â
   = (42.4)(17.6)(-1)
           Â
   = - 746.24 J
(d)
Work done by Gravity is,
Wg = Fd cos90
           Â
      = (mg)(0)
                 Â
= 0 J
I hope help you.....!!