A neutral metal sphere with radius R sits a distance d above an infinitely large sheet with charge +q. The magnitude of the gradient of the voltage within the sphere is:

NOTE: An infinitely large sheet cannot have a finite charge.  This question probably meant to say that the sheet had a charge density σ.

Also, writing a variable with a + in front of it does not designate that quantity as positive.  If q = −5C, then +q = −5C.  This question probably meant to say "sheet with charge density σ > 0."