A hollow conducting sphere of radius 15 cm has a uniform surface charge density $$+3.2\ \mu\text{C/m}^2$$. When a point charge q is placed at the centre of the sphere, the electric field at 25 cm from the centre just reverses its direction keeping the magnitude the same. Therefore, q is

A

$$+0.91\ \mu\text{C}$$

B

$$-0.91\ \mu\text{C}$$

C

$$+1.81\ \mu\text{C}$$

D

$$-1.81\ \mu\text{C}$$