What 4 digit number will always equal 8 if you ad or multiply all the digits together?

“…Did you just make that up for me, or was that something that existed beforehand? Because it’s certainly a riddle that suits Kid~ Also… this particular riddle marathon is for me to get it wrong and you to command something for if I do… You just wanting to give riddles? Hakuba mun has reasons for not saying a command, but that doesn’t mean you can’t.”