Please help

$${{\mathtt{x}}}^{{\mathtt{2}}} = {\mathtt{400}}$$

$${{\mathtt{x}}}^{{\mathtt{2}}}{\mathtt{\,-\,}}{\mathtt{400}} = {\mathtt{0}}$$

$$\left(\left({\mathtt{x}}{\mathtt{\,\small\textbf+\,}}{\mathtt{20}}\right){\mathtt{\,\times\,}}\left({\mathtt{x}}{\mathtt{\,-\,}}{\mathtt{20}}\right)\right) = {\mathtt{0}}$$

$$\underset{\,\,\,\,{\textcolor[rgb]{0.66,0.66,0.66}{\rightarrow {\mathtt{x}}}}}{{solve}}{\left(\begin{array}{l}{\mathtt{x}}={\mathtt{20}}\\ {\mathtt{x}}=-{\mathtt{20}}\end{array}\right)}$$

Take the square root of 400 to find x.