(1) How many of them got their first merit before the demotion of Junior Members in September last year?
(2) How many of those re-promoted to Junior Members got banned after that?
Too much to do

(3) How long it take from the days they got their first merits and promoted again to the days their accounts got banned?
I have no data on
when someone got banned.
Additionally, I still don't really get what you imply in those two figures.
You should make a note in the OP to state what they mean.
1. 45 (43.26%)
This means that user foserfox has merited 45 users who are now banned, which is 43.26% of the total number of users he merited. From
http://loyce.club/Merit/all_users_who_sent_Merit_2019-03-01_Fri_08.12h.txt:
325. 141 Merit sent by foserfox (#485194) to 104 unique users in 108 transactions