Question

Question in the link below.

Answer 1

We can suggest this equation:
5x=40º+x
5x-x=40º
4x=40º
x=40º/4
x=10º


Answer: x=10º

Answer 2

The 5x  and the combination of (40° + x) are "vertical angles".
Vertical angles are equal.
So
                                             5x = 40° + x

Subtract 'x' from each side:      4x = 40°

Divide each side by  4 :            x =  ?