Answer:
the answer is 9
Step-by-step explanation:
If you just try multiplying with every number, you'll eventually find the right one.
Since all angle measures in a triangle MUST equal 180°, we can set up an equation to solve for x.
[tex]13x + 2 + 5x - 7 + 3x - 4 = 180\\\\21x - 9 = 180\\\\21x = 189\\\\x = 9[/tex]
Our answer is x = 9.
