Solution:
A regular decagon is a 10-sided shape with equal side length.
The area A of a regular decagon is given as;
[tex]\begin{gathered} A=\frac{n\times a\times s}{2} \\ \text{Where;} \\ n=number\text{ of sides;} \\ a=\text{apothem}; \\ s=\text{side length} \end{gathered}[/tex]
Thus, the area of the regular decagon is;
[tex]\begin{gathered} A=\frac{10\times5\times3.25}{2} \\ A=81.25m^2 \end{gathered}[/tex]
FINAL ANSWER:
[tex]A=81.25m^2[/tex]
