Charges of $3\mathrm{.}0n{C}_r-2\mathrm{.}0n{C}_r-7\mathrm{.}0n{C}_r$ and $1\mathrm{.}0nC$ are contained inside a rectangular box with

length $1\mathrm{.}0m_r$ width $2\mathrm{.}0m_r$ and height $2\mathrm{.}5m.$ Outside the box are charges of $1\mathrm{.}0nC$ and $4\mathrm{.}0nC.$

What is the electric flux through the surface of the box?

Select one:

a$.-565N*\frac{m^2}{C}$

b$.170N*\frac{m^2}{C}$

c$.$ zero

d$.-340N*\frac{m^2}{C}$