how do u work out the arc length in a sector of a circle

The arc length, S, is given by

S = rΘ  where Θ is in radian measure

An alternative formula is

S = (Θ / 360) * 2 * pi * r    where Θ is in degrees

You follow the formula:

(θ/360) x πr^2

So, data divided by 360 times pi x radius squared.