we know that
The regular decagon can be divided into 10 congruent triangles
so
area regular decagon=10*[area of one triangle]
area triangle=b*h/2
where
b=3.25 m
h is the aphotem
h=5 m
area=3.25*5/2----> area=8.125 m²
area regular decagon=10*[8.125]----> 81.25 m²
Area=81.3 m²
the answer is
81.3 m²
