What do you mean by "How did they combine?"? You have found the two values of x that make the original expression true.
x = -2
$${{\mathtt{3}}}^{\left({\left(-{\mathtt{2}}\right)}^{{\mathtt{2}}}{\mathtt{\,-\,}}{\mathtt{2}}{\mathtt{\,\times\,}}\left(-{\mathtt{2}}\right){\mathtt{\,-\,}}{\mathtt{4}}\right)} = {\mathtt{81}}$$
$${{\mathtt{3}}}^{\left({\mathtt{2}}{\mathtt{\,\times\,}}{\left(-{\mathtt{2}}\right)}^{{\mathtt{2}}}{\mathtt{\,\small\textbf+\,}}{\mathtt{3}}{\mathtt{\,\times\,}}\left(-{\mathtt{2}}\right){\mathtt{\,\small\textbf+\,}}{\mathtt{2}}\right)} = {\mathtt{81}}$$
x = -3
$${{\mathtt{3}}}^{\left({\left(-{\mathtt{3}}\right)}^{{\mathtt{2}}}{\mathtt{\,-\,}}{\mathtt{2}}{\mathtt{\,\times\,}}\left(-{\mathtt{3}}\right){\mathtt{\,-\,}}{\mathtt{4}}\right)} = {\mathtt{177\,147}}$$
$${{\mathtt{3}}}^{\left({\mathtt{2}}{\mathtt{\,\times\,}}{\left(-{\mathtt{3}}\right)}^{{\mathtt{2}}}{\mathtt{\,\small\textbf+\,}}{\mathtt{3}}{\mathtt{\,\times\,}}\left(-{\mathtt{3}}\right){\mathtt{\,\small\textbf+\,}}{\mathtt{2}}\right)} = {\mathtt{177\,147}}$$
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