Your question is Bash Log Parsing and Firewall Blocklist. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Write a bash script that parses a log file, extracts specific IP addresses with more than 100 failed login attempts, and appends them to a firewall blocklist.