2x < - x + 20 + 7 i don't get how to answer this question

What is the average rate of change for this function for the interval from x=2 to x=4 ?

Monthly water bills for a city have a mean of $108.43 and a standard deviation of $32.09. find the probability that a randomly selected bill will have an amount greater than $155, which the city believes might indicate that someone is wasting water. would a bill that size be considered unusual?

Name each raycalculation tip: in ray "ab", a is the endpoint of the ray.