We can use the vertical angle theorem which states that any two opposite angles are congruent. So, you can just set the two measures equal to each other and solve for x:
[tex]7x-99=2x+1[/tex]
[tex]5x-99=1[/tex]
[tex]5x=100[/tex]
[tex]x = \frac{100}{5} = 20[/tex]
So, your answer is 20°.
