Answer: 45 red marbles
Explanation:
Using the ratios, we can create a fraction for the number of marbles.
3/5 of the bag would be red marbles, and 2/5 of the bag would be blue marbles.
(you get the 5 from adding 3+2 together)
If you take 3/5 of 75, you would get 45 red marbles.