Plz help! Gonna need to turn it soon

Which of the following is most likely the next step in the series? a3z, b6y, c9x, d12w, е15v, f18u

40 describe the outliers from the scatter plot.

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?