Let the measure of angle XAY = x = angle BAC
Then, because AX = XY, then the measure of angle XYA also = x
And, by the exterior angle theorem , angle BXY = 2x
And since XY =TB, then angle XBY also equals 2x
So angle XYB = 180 - angle BXY - angle XBY = 180 - 2x - 2x = 180 - 4x
And the sum of angle XYA + angle XYB + angle BYC = 180
So x + 180 - 4x + angle BYC =180 (1)
So, rearranging (1)....... we have that angle BYC = 3x
And since YB = BC, then the measure of angle BCY also = 3x = angle BCA
And in triangle BAC, the sum of angles BAC + angle ABC + angle BCA =180
So
x + 120 + 3x =180
4x + 120 = 180
4x = 60
x = 15° = angle BAC