I learned how to solve this in geometry in middle school, but I can't remember. This isn't homework.
I want to calculate the distance between points $A$ & $B$ and the arc $\widehat {AB}$ as well. The know values are, the radius $R$ and the $S$ length. $C$ is the center of the circle. The angle is not important, but it's probably involved in the arc calculation.
$R=6400$
$S=30$
$\widehat {AB}=?$
this values are arbitrary, I only want to know how to solve.