HELP! Confused about this set of related questions

#1
Hi, I'm stumped on this set of questions. I know it must be very simple, but I can't seem to crack it... Anyone able to give me some direction/Excel help to solve these? I'd be happy to do my own work, if anyone can confirm with me what the right answers are so I can replicate in Excel.

Use the following information to answer questions

Suppose the machine that seals the cereal boxes operates for an average of 13 days before it breaks down. Assume the machine has just been serviced and is in good running order.

A: What is the probability that the machine works for 13 days before it breaks down?

B: What is the probability that the machine works between 5 to 15 days before it breaks down?

C: What is the probability that the machine will operate longer than 20 days?