Given :
∠ABF = ( 7x + 20 )°
∠FBC=(2x - 5)°
∠ABC= 159°
To Find :
The value of x .
Solution :
Assuming B the center of a circle .
So , all three given angles must be added to 360° .

Therefore , the value of x is 20.67° .
Hence , this is the required solution .