5 + 3r = 5r - 19

I need to solve for "r" and i can't think please help
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What expression is equivalent to 42x-56y

Standard deviation of 19,29,21,22,23

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?