Hi! Please help me with this question. Thank you!

{11 no points}: Assume there are n keys and onlyr one unlocks the door in front of you but uou do not know which one. You rst tru one key and if it does not work uou put it aside and try another key. 1l'ou repeat the prooess until the door is unlocked. a]: Find the expression for the probability that you will need at least m attempts. b} Now assume that you pick a keu. tru. and then return it to the table. The keys are then mixed randomly, and you repeat the process. Repeat part a}