Answer
See the detailed answer below.
Work Step by Step
$$\color{blue}{\bf [a]}$$
An infinite charged line with a linear charge density of $2\times 10^{-7}$ C/m exerts an electric field of 25,000 N/C at a distance of $r$. Find $r$.
$$\color{blue}{\bf [b]}$$
Solving the given formula for $r$,
$$r=\dfrac{2(9\times 10^9)(2\times 10^{-7})}{25,000}=\color{red}{\bf 0.144}\;\rm m$$
