Let

the number of green,

the number of yellow and

the number of blue marbles respectively.
We have

(we will call this equation 1)
Also,

(yellow marbles are three times as many as blue marbles), so equation 1 becomes

But,

(green marbles are as many as blue marbles - 90)
and because

, we have that

So, equation 1 is now


We add 90 to both sides so

We divide each side by 7, so finally

and we have

and

To check if our results are correct, we can see that

,
so we are indeed correct.