We can always split a regular polygon with [tex] n [/tex] sides into [tex] n [/tex] triangles, whose base is the side of the polygon and whose height is the apothem of the polygon. So, the sum of the areas of all these triangles is
[tex] A=n\times \dfrac{s\cdot a}{2} [/tex]
where [tex] n [/tex] is the number of sides, [tex] s [/tex] is the side length, and [tex] a [/tex] is the apothem length.
So, you just need to plug you values in: in your case, you have [tex] n=7,\ s=6,\ a=8 [/tex]
So, the formula becomes
[tex] A=7\times \dfrac{6\cdot 8}{2} = 7 \times 6\cdot 4 = 168 [/tex]
