Unit rate means one. So the best way to solve this is using a proportion over one. If there are 258 pencils in 3 purses 258/3 then how many are in one purses x/1. Cross multiply next.
258/3 * x/1. You get 3x and 258. To get the x alone, divide both sides by three. Your answer is 86 pencils in one purse.
