Planes $x=2$ and $y=-3,$ respectively, carry charges $10n\frac{C}{m^2}$ and $15n\frac{C}{m^2}.$ If the line $x=0,z=2$ carries charge $10n\frac{C}{m},$ calculate $E$ at $(1,1,-1)$ due to the three charge distributions.

In this question i want someone to explain how did we get the vector ay

And explain points on surface charge distrbutin

because i wonder why isn't $4$ay because the jumping between the charge and main point