Length of boundary of the part = 288 m (given)

Length of boundary = circumference of semi circle + diameter = pie * radius + 2 * radius

Radius * ( pie + 2 ) = 288

Radius = 288 / ( 22/7 +2 )

= 288 / ( 36/7 )

= 288 * 7/36

= 8* 7 = 56 m

Area of circle = pie * r^2 = 22/7 * 56 * 56 = 22 * 8 *56 = 9856 m^2