Help and please make sure it’s right :)

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

its totaly b

your welcome btw