How can I tell a graph represents a function?

You are at a restaurant and owe $38 for your meal. you want to leave a 20% tip. how much will your tip be?

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? probability distribution px(x) 6 hours 7 hours 8 hours 9 hours 10 hours 0.62 0.78 пол

How do i simply this expression (quadratic formula basis) on a ti-84 or normal calculator?