Answer
${\bf 0.16}\;\rm V/m$
Work Step by Step
The current density is given by
$$J =\dfrac{I }{A }=\sigma E$$
hence,
$$E=\dfrac{I }{A \sigma}$$
$$E=\dfrac{I }{\pi r^2 \sigma_{\rm iron}}$$
Plug the known;
$$E=\dfrac{(5)}{\pi (1\times 10^{-3})^2 (1\times 10^7)}$$
$$E=\color{red}{\bf 0.16}\;\rm V/m$$
