The formula for the area of a triangle is: $\displaystyle{A}={\left(\frac{{1}}{{2}}\right)}{b}\cdot{h}\usepackage{cmbright}\Huge\$

Substitute the values $\displaystyle{b}={21}\usepackage{cmbright}\Huge\$ and $\displaystyle{h}={12}\usepackage{cmbright}\Huge\$ :

$\displaystyle{A}={\left(\frac{{1}}{{2}}\right)}{21}\cdot{12}={\left(\frac{{1}}{{2}}\right)}{252}={126}\usepackage{cmbright}\Huge\$

The area of the triangle is 126 square meters.