Many candidates messed up with the calculations of the cross-sectional area of the wire as they could not convert millimeters to metres and in the poor handling of the standard form (decimals) Not much difficulty was encountered with the correct formula and computation for strain.
The expected answers are:
(a)        Stress = Force = F
                            Area    A
            
          =        40
3.14 (1.0 X 10-3)2
= 1.27 X 10-7 Nm-2
(b)       Strain = Extemion or       e
                           Length                l
= 0.24 X 10-3
3
= 8.0 X 10-5