Step-by-step explanation: First off, you set up your equation. This equation will be 57+4x+4+7x+9=180. The reason why we put all those angles equal to 180 is because the 3 angles of a triangle always have a sum of 180. The equation is just made up of all those angles put together. Next you combined like terms. You would add 7x & 4x to get 11x. You would add 57, 9, & 4 together to get 70. Now you have the equation 11x+70=180. You will subtract 70 from itself to get 11x by itself. But what you do to one side you got to do to the other. So you subtract 70 from 180 aswell. That gives you 11x=110. Now to finish the problem, you divide 11x by 11 & 110 by 11. That will give you x=10.
