x=42
Coresponding angles of similar triangle are congruent.
To find the missing angle of the triangle on the right you conplete the equation 180-126-16, which equals 38.
Since congruent angles of similar triangle are congruent, the leftmost angle on the triangle to the right is also 38.
After that you have to solve the equation:
180=16+38+3x.
180=54+3x
-54 -54
126=3x
/3 /3
42=x