For this problem we use the arcs and chords theorem we know that
[tex]\begin{gathered} \measuredangle H\text{EF=}\frac{1}{2}(mGF+mDH) \\ \text{Substituting }\measuredangle HEF=10x-22,\text{ mGF=5x+9 and mDH=11x+7 we get} \\ 10x-22=\frac{1}{2}(5x+9+11x+7) \end{gathered}[/tex]
Solving for x we get:
[tex]\begin{gathered} 10x-22=\frac{1}{2}(16x+16)=8x+8 \\ 2x=30 \\ x=15 \end{gathered}[/tex]
Finally, we substitute x for mDH=(11x+7) degrees=(11*15+7) degrees=172 degrees.
mDH=172 degrees.
