$(60$ points$)$ For the NFA shown below, find a regular expression corresponding to the language it accepts.

$(40$ points$)$ Prove that language $L$ is non$-$regular. $L=\{\begin{array}{ccc}\text{w}\text{i}\text{n}& \{0,& 1{\}}^{*}|w\end{array}$ contains the same number of $0s$ sand $1$ s