[tex]\begin{gathered} \text{ the sum of internal angles of a polygon is } \\ \mleft(n-2\mright)\times180,\text{ where n is the number of sides!} \\ \\ \text{For this polygon, the sum is} \\ (4)180=720,\text{ Thus} \\ x+115+105+116+137+139=720 \\ x+612=720 \\ x=720-612 \\ x=108 \\ \\ \text{We have that x=108} \end{gathered}[/tex]
