Answer:
The blank in the equation is 1.
x = 7 and the vertical angles measure out to 64 degrees.
Explanation:
When solving for x, you always want to keep the variables on one side. So you'll subtract 9x from both sides. That gives you 1=3x-20. Then you'll add 20 to both sides. This gives you 21=3x. After you'll divide by 3 on both sides. This gives you 7=x.
Now you'll plug in 7 for x. This gives you 12*7-20=9*7+1. First, you'll multiply which gives you 84-20=63+1. Add and you'll get 64 on both sides.