In order to solve you must find the value of the blank angle.
Here is your first equation.
126 + x = 180
Subtract 126 from both sides.
x = 54
So now add up all the angles.
x + (2x + 6) + 54 = 180
Combine like terms.
3x + 60 = 180
Subtract 60 from both sides.
3x = 120
Divide.
x = 40
Now check your answer.
40 + 2(40) + 6 + 54 = 180
40 + 80 + 6 + 54 = 180
120 + 60 = 180
180 = 180
There is a solution. The answer is 40.
I hope this helps love! :)