Answer:
21
Step-by-step explanation:
Hey There
So remember all of the angles in a triangle add up to equal 180
The exterior angle is equal to the missing interior angle because they are vertical angles
so 180 = 2x + 6 + x + 9 + 129
step 1 combine like terms
6+9+129=144
2x+x=3x
now we have
180=144+3x
step 2 subtract each side by 144
180-144=36
now we have
3x=36
step 3 divide each side by 3
36/3=12
Now we just plug in 12 to x+9
12+9=21
so we can conclude that angle A = 21
