You can make a square by joining the centers of the adjacent circles. The circle would have sides 10m. So the area of that square would be 100m^2.

Inside the square is four quarter circles, so the area of those four quarter circles is the area of one circle which is PI * R*2 = 25 PI m^2

The remaining area is the empty space = 100m^2 - 25 PI m^2, where PI = 3.14 = 21.5 m^2.