Ok, the formula to find the area of a regular polygon is...
A = 1/2 nsr
In this equation...
n = number of sides s= side length r = apothem (radius of the inscribed circle)
To find the area, we must first find the apothem. The apothem is the radius of the inscribed circle (draw a line from the center of the figure to the center of one of the sides). If you draw the apothem in to the figure, it creates a right triangle with a hypotenuse of 13.07 in and one side length of 5 in (1/2 of the figure's side length). Now we can find the apothem with the formula