Use the idea that $\dfrac{\text{arc length}}{\text{circumference}} = \dfrac{\text{central angle}}{360}$. Plug in the central angle and the circumference from the problem.

Once you know what fraction of the circle the 60° angle represents, multiply that fraction by the total circumference, 24, to get the arc length.

In Desmos, type (60/360)*24. The value that Desmos outputs is the length of minor arc $\widehat{AB}$.

For a circle, the length of an arc is proportional to the central angle that intercepts it. This relationship can be written as:

Here, the central angle is $60^\circ$ and the circumference is 24.

Compute the fraction of the full circle that a $60^\circ$ angle represents:

So, minor arc $\widehat{AB}$ is $\tfrac{1}{6}$ of the full circumference.

Use the fraction $\tfrac{1}{6}$ of the full circumference 24 to find the arc length:

So the length of minor arc $\widehat{AB}$ is 4, which corresponds to choice B.