check the picture below.
the lateral area, namely the area of the sides, in this case will be the area of all the triangular faces of the OCTAgonal pyramid, OCTA=8, so there are 8 of them.
now, each triangular face, has a base of 5 and a height of 6√2, so we simply get the area of each triangle and sum them up,
[tex]\bf \stackrel{\textit{area of the 8 triangles}}{8\left[ \cfrac{1}{2}(5)(6\sqrt{2}) \right]}
[/tex]
