Actually Welcome to the concept of Equilateral triangles.
Since the above triangle is a equilateral triangle, that has all sides equal and also all angles are equal,
by applying the angke sum property of triangle we get as,
==> 6x + 6x + 6x = 180°
hence, 18x = 180°
==> x = 180/18 ==> 10°
hence the value of x = 10°