2028. Find Missing Observations

You have observations of n + m 6-sided dice rolls with each face numbered from 1 to 6. n of the observations went missing, and you only have the observations of m rolls. Fortunately, you have also calculated the average value of the n + m rolls. You are given an integer array rolls of length m where rolls[i] is the value of the ith observation. You are also given the two integers mean and n. Ret