We have to simplify the ratios to make them comparable;
If the ratio of green to yellow marbles is 2 to 5 and
The ratio of yellow to orange marbles is 3 to 4.

Now we can rewrite the ratios of green: yellow : orange as

From this, we can see that the ratio of green to orange marbles is;

Therefore, the ratio of green to orange marbles is 3 : 10