Correct. $\displaystyle\angle{G}{K}{J}\usepackage{cmbright}\Huge\$ is a straight angle, so its measure is $\displaystyle{{180}}^{\circ}\usepackage{cmbright}\Huge\$ . Therefore:

$\displaystyle{{50}}^{\circ}+{m}\angle{H}{K}{I}+{{42}}^{\circ}={{180}}^{\circ}\usepackage{cmbright}\Huge\$

so $\displaystyle{m}\angle{H}{K}{I}={{180}}^{\circ}-{{50}}^{\circ}-{{42}}^{\circ}={{88}}^{\circ}\usepackage{cmbright}\Huge\$