A spherical conductor of radius 10 cm has a charge of 3.2 x 10⁻⁷ C distributed uniformly. What is the magnitude of the electric field at a point 15 cm from the center of the sphere?

a) 2.56 x 10⁴ N/C
b) 1.28 x 10⁴ N/C
c) 2.56 x 10³ N/C
d) 1.28 x 10³ N/C