Help! I need to know how to solve this

Every triangle measures 180 degrees.
In order to get the answer you need to add every equation and set it equal to 180.

2x+4+2x-9+x=180
Combine like terms.
5x-5=180
Add 5 to the other side.
5x=185
Divide by 5.
x = 37

Now, plug 37 in for every x.
Angle A: 2(37)-9
Angle B: 2(37)+4
Angle C: 37

The measures are:
Angle A = 65
Angle B = 78
Angle C = 37

Hope this helps!

20 percentage, you can also do it on a calculator.