[tex]Area\ of\ pyramide=area\ of\ square+4\cdot\ area\ of\ triangulars\\\\A_p=a^2+4\cdot\frac{ah}{2}\\\\a^2=25\\a=5\\\\105=25+4\cdot\frac{5h}{2}\\105-25=2\cdot5h\\80=10h\ \ \ \ |:10\\h=8\\\\A_t=\frac{5\cdot8}{2}=\frac{40}{2}=20\ ft^2\\\\Each\ triangular\ has\ 20\ ft^2[/tex]
