In the given electric field E→=[α(d+x)i^+E0j^]NC−1; where α=1  NC−1 hypothetical closed surface is taken as shown in figure.The total charge enclosed within the close surface is

ϕABCD=−acd  unitϕCDEF=−bcE0 unitϕABEF=bcE0+c∫0a(d+x)dy=+bcE0+acd+c∫0axdy=+bcE0+acd+cab∫0bxdx [Since  xb+ya=1  or  dxb=−dya]=[+bcE0+acd+acb2]unitUsing Gauss's law, we getϕnet=qinε0  or   qin=abcε02