I need help understanding these problems.

For problems like number 9, solve for the x's first (or whichever variable there's more of) you should solve for the x's like you did for the first problem, then set the equation to an A+B=180 format. The reason for this is two angles (in some cases more) on a straight line together will always equal 180 degrees.
For 10. set the equations with x in them to that A+B=180 format. Then once you've found x plug it into 6x-7. When you have that answer set 8y+17 equal to the answer you got and solve for y.
For 11 and 12. These ones can be a bit more complicated because of their visual appearance, however you just need to combine the earlier steps taken to solve the first couple of equations.
Beginning with 12. If you ever see a Z pattern, know that the sides facing > and < ( the inside angles of the Z) are equal to each other. So you set the equations with x equal to each other, and once you get x plug it into the equation inside of the triangle. Since you've already been given 90, set the equation up like this: 43+90+(7y-20)=180. Because all the angles in a triangle are equal to 180 degrees. Then just solve for y. y=9
Lastly for number 11. This one is by-far the hardest of all of them. You have to adjust how you look at the problem. You'll see that if you add (3x+49) it's actually congruent to (7x-23). once you figure out x you should then plug x into 3x giving you 54. The set up the equation like this 11y-1=54. That will give you y=5.