∠2 and ∠3 are alternate interior angles. In order to A II B, the alternate interior angles must be equal.
Then,
![\begin{gathered} \angle2=\operatorname{\angle}3 \\ 3x-10=x+30 \end{gathered}]()
To find x, subtract x from both sides of the equation:

Now, add 10 to both sides of the equation:

Finally, divide both sides by 2:

Answer: x = 20.