You get $\displaystyle{\left(\frac{{2}}{{7}}+\frac{{1}}{{3}}\right)}+\frac{{3}}{{4}}\usepackage{cmbright}\Huge\$ by applying the commutative property to the first addition. Then you get $\displaystyle\frac{{2}}{{7}}+{\left(\frac{{1}}{{3}}+\frac{{3}}{{4}}\right)}\usepackage{cmbright}\Huge\$ by using the associative property to regroup.