Find the length of the arc s in the figure. (Assume r = 3 and θ = 100°.)

I don't see a pic, but  the arc length - S - is given by :

S  = r * (theta)      where theta is in rads

So.....I  assume you have

S = 3 * ( 100 * pi / 180)  =  about 5.236   units