Ineed the answer to 2a+b-a+3b it's in the maths section of my homework and i'm struggling to answer it

There are three bags: a (contains 2 white and 4 red balls), b (8 white, 4 red) and c (1 white 3 red). you select one ball at random from each bag, observe that exactly two are white, but forget which ball came from which bag. what is the probability that you selected a white ball from bag a?

Find y to the nearest hundreds place

Im so bad at fractions they are not my best math thing to work on