Answer:
The latest 2.5% of bills will be received in 20 more days after mail-out.
Step-by-step explanation:
We are given the following information in the question:
Mean, μ = 31 days
Standard Deviation, σ = 6 days
We are given that the distribution of The number of days (X) is a bell shaped distribution that is a normal distribution.
Formula:


We have to find the value of x such that the probability is 0.025

Calculation the value from standard normal z table, we have,

Hence, the latest 2.5% of bills will be received in 20 more days after mail-out.