ANSWER
mFJH = 210º
EXPLANATION
The measure of an arc is twice the measure of the inscribed angle subteded by it:
[tex]\text{mFJH}=2m\angle FGH[/tex]
First we have to find x:
[tex]17x-28=2(6x+21)[/tex]
Apply distributive property of addition on the right side:
[tex]\begin{gathered} 17x-28=2\cdot6x+2\cdot21 \\ 17x-28=12x+42 \end{gathered}[/tex]
Now we have to get the x together on the same side of the equation. To do that we have to subtract 12x from both sides:
[tex]\begin{gathered} 17x-12x-28=12x-12x+42 \\ 5x-28=42 \end{gathered}[/tex]
Now, add 28 to both sides:
[tex]\begin{gathered} 5x-28+28=42+28 \\ 5x=70 \end{gathered}[/tex]
And finally divide both sides by 5:
[tex]\begin{gathered} \frac{5x}{5}=\frac{70}{5} \\ x=14 \end{gathered}[/tex]
Now, with x = 14, we just have to replace it into the expression for the measure of arc FJH:
[tex]\begin{gathered} \text{mFJH}=17x-28 \\ \text{mFJH}=17\cdot14-28 \\ \text{mFJH}=238-28 \\ \text{mFJH}=210 \end{gathered}[/tex]
The measure of arc FJH is 210º
