Addy has five times more blue marbles than red marbles. she has twice as many red marbles than green marbles. she has 6 red marbles. which number sentence could be used to find the number of green marbles?

I would say it is B. 6 X 5 =30

So you have 6 marbles and 6 is twice as many as however many green marbles you have. The "five times more blue marbles than red marbles" is used to confused you, it's irrelevent to solving the problem.  For the answer, if you use the opposite equation of multiplication, division, it'll give you the answer. I believe doing that is called inverse something, but I can't remember atm ꒪▿꒪

So I'm quite certain it's C.