Answer:
21
Explanation:
There are two parallel lines given.
Two transversals cut them.
Here m and n are parallel.
Two transversals cut them so that a triangle is formed.
Let us use the property that sum of angles of a triangle = 180
Bottom angle of triangle = 39 (vertically opposite angles)
Top left angle = 4x+3 (vertically opposite angles)
Top right angle = 180-6x (linear pair property)
Now add these 3 and equate to 180
39+4x+3+180-6x = 180
2x = 42
Or x = 21