Answer:
800 blue marbles
Explanation:
Since the ratio of red to blue is 3 to 4, we know that there is 600 red marbles.
Using this information we know that 3 and 600 are both red marbles, now we multiply 3 by 200 to get a total of 600 red marbles. You can also find the value needed to multiply the 3 by dividing 600 by 3.
Since we know that 1 ratio is 200, we multiply 4 by 200 to get 800 blue marbles.