The two angles are alternate external, because they are on the external side of the parallel lines and on alternate sides of the transversal one. This means that they are congruent. So we can find the value of x by making their expressions equal and solving for x.
[tex]\begin{gathered} 4x=3x+30 \\ 4x-3x=30 \\ x=30 \end{gathered}[/tex]
The value of x is 30°
