# Electric potential inside conductor derivation

Hey, i have this question:
The electric potential inside a charged spherical conductor of radius R is given by V = keQ/R and outside the conductor is given by V = keQ/r. Using E=-dV/dr, derive the electric field inside this charge distribution.

Alright, so I started to find the derivative of the formula for the potential outside the conductor, however Ke, and Q are constants. Therefore E=-KeQ. Subbing into the first formula, to solve for the potential inside the sphere, i got E= -V/R. Sounds good?
well, when i submit my answer, it says it needs a numerical answer, did i go wrong somewhere?
Brent