A= \(0.8m^2\) d= 20mm =\(\frac{20}{1000}\) = 0.02m

v =120v; \(ε_oA\)= \(8.85 × 10^-12 fm^-1\)

C = \(\frac{ε_oA}{d}\)

C =\(\frac{8.85 × 10^-12×0.8}{0.02}\)

C= \(3.54 × 10^-10 F\)

Q= CV

⇒ \(3.54 × 10^-10\) × 120 = \(4.25×10^-8c\)

Q=\(42.5 × 10^-9c\) = 42.5nC



There is an explanation video available below.