Check the picture below.
since the pyramid has 4 triangular faces and a square base, let's add their areas together and that'd be the area of the pyramid.
[tex]\stackrel{\textit{\Large total area}}{\stackrel{base}{(12\cdot 12)}+\stackrel{4~triangles}{4\left[\cfrac{1}{2}(12)(6\sqrt{3}) \right]}}\implies 144 + 144\sqrt{3}~~\approx ~~393.42[/tex]
