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.
First, find 1/2 of 3. That is 1.5 gallons. Since there are 4 quarts in a gallon, do 1.5*4 to get 6.
The answer will be reflect (2, - 3 ) in x = -1