A Physics Instructor in an Anteroom Charges an Electrostatic Generator $\mu$

A physics instructor in an anteroom charges an electrostatic generator to 25 $\mu$ C, then carries it into the lecture hall. The net electric flux in N . m²/C through the lecture hall walls is:

A) 0
B) 25 *10^-6
C) 2.2 * 10⁵
D) 2.8 * 10⁶
E) can't tell unless the lecture hall dimensions are given