-18y+7yz-4z
(simply the expression)
please help

Find the value of the variable and the length of each secant segment

8000 + 8800 + 8000 + 8 million + 80 trillion + another a katrillion equals

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?