For a polygon, the SUM of the internal angles is (n-2) * 180 (n=6 for hexagon)
(6-2)*180 = 720 Thus EACH angle is : 720/6 = 120 degrees
So the large angle of the triangle is 120 degrees the other two are equal to each other
there are 180 degrees in any triangle:
(180-120) / 2 = 30 degrees for each of the smaller angles.
Now use the law of sines
10/sin30 = x/(sin120)
10/(.5) * (sqrt3 )/ 2 = x
10 sqrt 3
10/sin30 * sin 120 = 17.32