Plese help:

{b} The following process leads to a rule for determining if a large number n is divisible by 1?: - Remove the last digit, it, of 11 leaving a smaller number a. I Let H! = H - 5E1. - Repeat with n'r in place of it. So, for example, if n = 12345, then 11' = 1234 5 - 5 = 1209. Repeating would create12D-5-92 ?5;?-5-5 = -18; and so on. {i} Prove that 1T|n if and only if l?|n'. {6 marks] Tl'nis shows that we can repeat the process with n', and so on, until we reach a "small enough" value that checking divisibility' by 1? is straightfonvard. [ii] Give, with justication, an asymptotic upper bound in terms of n, for the number of times this process needs to be repeated before a negative 12' is reached. {4 marks]