Find the size of x in the diagram.

The image shows two angles, $2x$ and $4x$, that lie on a straight line. Angles on a straight line are supplementary, meaning their sum is $180^\circ$.

Add the two angles and set their sum equal to $180^\circ$:

Combine the like terms on the left side of the equation:

Divide both sides by 6 to find the value of $x$:

Substitute the value of $x$ back into each expression:

• First angle: $2x = 2 \times 30^\circ = 60^\circ$
• Second angle: $4x = 4 \times 30^\circ = 120^\circ$

The size of $x$ is $\boxed{30^\circ}$.