Pardon the handwriting

Try drawing a model to visualise. Do take not thay the fraction of red is of the whole bag, and you want the ratio of red to blue.

You will then get two diff equations based on R and B, the number of red and blue balls. You can subtract one equation from another and you will take out B, leaving only R in the equation.

You can solve R, and then solve B. You can try checking your answers by working it out again with the known answers.

Go try it out! Hope it helps