Please help me with this!!

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

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?

If f(x) = x+8 and g(x) = 4x- 3, find (f+g)(x)