I dont know porportion method but I can help you this way! If you have 24 pens, thats 2 dozen, and 10 of those pens cost 3 dollars. Well first you would divide 3.00 by 10 because you need to find out how much each pen cost. 3.00/10 is 0.3. So each pen costs 0.3. So now that you know each pen costs 0.3 cents, you can do 0.3 x 24 because of your 2 dozen pens. Which is 7.20. Then it says mow much MORE does it cost for 2 dozen pens. So if 10 pens cost 3.00 and 24 pens cost 7.20, then you subtract 7.20-3.00 and you get 4.20. That should be your answer
