Use the radius of the circle, $\displaystyle\frac{{20}}{{2}}={10}\usepackage{cmbright}\Huge\$ , to find the area of the circle:

$\displaystyle{A}=\pi{{r}}^{{2}}=\pi{{\left({10}\right)}}^{{2}}=\pi\cdot{100}\approx{3.14}\cdot{100}={314}\usepackage{cmbright}\Huge\$ square meters

The area of the triangle is: $\displaystyle{A}=\frac{{1}}{{2}}{b}\cdot{h}=\frac{{1}}{{2}}\cdot{56}\cdot{56}=\frac{{1}}{{2}}\cdot{3},{136}={1},{568}\usepackage{cmbright}\Huge\$

The area of the shaded region equals the area of the triangle minus the area of the circle. This is approximately $\displaystyle{1},{568}-{314}={1},{254}\usepackage{cmbright}\Huge\$ square meters.