Electric field

Electric field along the line passing through two point charges, A point charge Q1= +3 micro C is placed at the origion and a point charge Q2= -7 micro C is placed at x=0.4m on the x-axis of a cartesian co-ordinate system.
a) Determine the electric field E(x)=E(x) x^ (unit vector) at the point along x_axis.
b) Plot E(x) vs x for x<0