C=2πr and the circumference is measured at 360°
So if we were to set up a proportion we could say:
s/(2πr)=α/360
α=180s/(πr)
We are given that s=4m and r=13m so:
α=180(4)/(13π)
α=720/(13π) m which is approximately:
α≈17.63°
Which is why radians are often used, because in radians...
α=[720/(13π)](π/180)
α=4/13 rads
Or the arc length in radians is simply expressed as:
s=rα
α=s/r (which is much neater :P) then it is plain to see that:
α=4/13 rads
