Perhaps you thought that $\displaystyle\angle{Y}{V}{X}\usepackage{cmbright}\Huge\$ was the same size as $\displaystyle\angle{Y}{V}{Z}\usepackage{cmbright}\Huge\$ . The four angles along the straight angle have measures that total $\displaystyle{{180}}^{\circ}\usepackage{cmbright}\Huge\$ . Find the sum of the three given angles and then subtract that sum from $\displaystyle{{180}}^{\circ}\usepackage{cmbright}\Huge\$ .