Walker, Halliday & Resnick — Gauss' Law: Problem 16

16 Two large metal plates of area $1.0\text{ m}^2$ face each other, $6.0\text{ cm}$ apart, with equal charge magnitudes $|q|$ but opposite signs. The field magnitude $E$ between them (neglect fringing) is $72\text{ N/C}$. Find $|q|$.