We are given a triangle that is split into two right angled triangles
The source triangle has been identified to be an equilateral triangle with all sides and angles equal.
Since all the internal angles in an equilateral triangle equals 180 degrees, we then know that:
60 + 60 + x + x = 180 degrees
Adding up like terms give:
120 + 2x = 180
Subtracting 120 from both sides gives:
2x = 180 - 120
2x = 60
Dividing both sides by 2 gives:
x = 30 degrees