Once you know what fraction of the full circle the 60° represents, apply that same fraction to the total circumference, which is 30.

Multiply the fraction you found by 30. Double-check your multiplication and any simplification of the fraction.

In Desmos, type (60/360)*30 or equivalently 30*(60/360) into the expression line. The output is the length of the minor arc $\widehat{AB}$; read that value directly from Desmos.

A full circle has $360^{\bullet}$. The central angle $\,\angle AOB = 60^{\bullet}$ is part of that full circle.

So the fraction of the circle that this angle represents is:

Simplify $\frac{60}{360}$:

So the arc $\widehat{AB}$ corresponds to $\frac{1}{6}$ of the entire circle.

The total circumference of the circle is 30, and the minor arc $\widehat{AB}$ is $\frac{1}{6}$ of the circle.

So the length of arc $\widehat{AB}$ is:

Therefore, the length of minor arc $\widehat{AB}$ is 5.