a=?

s=10.5cm
A= 19,887.5cm squared

Pentagon

A=asn/2
19,887.5cm=a*10.5*5/2
39775=52.5a
a=757.61cm?
am i correct?

regular nonagon
a=9.6cm
A=302.4cm squared
find perimeter thanks!

302.4cm^2