Email - Your bank network is hacked...

Hey guuuuys!

Im trying to get an practicant vacancy in IT security at bank…
They sent me a question to decide whether i go to the next part – interview or not…
HELP ME PLEASE!!

The question roughly is –

You work in a bank as IT security specialist and you recieve an email from anonymous sender that reads "Your bank network is hacked"
1) What do you do in this situation to make sure if network is really hacked or its fake?
2) What do you do if you discover that networks and systems is hacked?


PLEASE HELP, THANKS A LOT!! <3