54 degrees
The sum of interior angle of a triangle is 180 degrees. Let the unknown measure be "x" such that
[tex]\begin{gathered} x+120+6=180 \\ x+126=180 \end{gathered}[/tex]Subtract 126 from both sides
[tex]\begin{gathered} x+126-126=180-126 \\ x=180-126 \\ x=54^0 \end{gathered}[/tex]Hence the measure of the third angle will be 54 degrees
