Julie has a bag of p blue marbles and q red marbles in the ratio 2: 3. she adds r blue marbles. the ratio of blue marbles to red marbles is now 2: 1. what is the ratio between p and r

I'm not sure how to answer the question... BUT, I know that the side that says 2 is for the blue marbles and 1 is for the red marbles, meaning that every 2 blue marbles she has equal 1 red marble. 
Sorry I didn't have the answer, hope this helps :/

$7.50x+$4.50y=midk it's been awhile since i've done one of these