Answer:
105
Explanation:
Using basic algebra and the fact that the sum of all angles in a triangle always equals 180, we find that X = 21
Multiply 21 by three to find the value of 3x, which is 63
Add 12 to 63: 75
We also know that the angle of a straight line is also 180, so we subtract 75 from 180 to find ? which is 105
Hope this helps :)