Why are these rows equivalent? are they even equivalent? please tell me the right answer. 7a+5b−3a+4b
7a+5b+(-3a)+4b

The human resources manager at a company records the length, in hours, of one shift at work, x. he creates the probability distribution below. what is the probability that a worker chosen at random works at least 8 hours? 0.62 0.78 0.84 0.96