`` The electric field at the distance d away from the point charge is given by
`E = k q/d^2`
where `k` is the constant: `k = 8.99*10^9 (N*m^2)/C^2`
Thus, the magnitude of the point charge is
`q = (E*d^2)/k`
Plug in the values for E and d, making sure to convert d = 5 cm into meters: d = 0.05 m.
`q = ((100 N/C) *(0.05 m)^2)/(9*10^9 (N*m^2)/C^2)=2.8*10^(-11) C`
The magnitude of the charge is `q=2.8*10^-11 C`