Answer
We can rank the spheres according to the magnitude of the electric field they produce at point P:
$(a) = (b) \gt (c) \gt (d)$
Work Step by Step
We can draw a spherical Gaussian surface at point P around the center of each sphere.
We can write an expression for the electric field on the surface:
$E = \frac{1}{4\pi~\epsilon_0}~\frac{q_{enc}}{r^2}$
Note that $r$ is the same for all four Gaussian surfaces.
For (a) and (b), the enclosed charge is $Q$
The enclosed charge in (c) is less than $Q$, and the enclosed charge in (d) is less than the enclosed charge in (c)
We can rank the spheres according to the magnitude of the electric field they produce at point P:
$(a) = (b) \gt (c) \gt (d)$
