please explain with steps as I did not understand the other solutions provided on chug, assume you can use a scientific calculator with explaining what to do on them

2. A system allows the user to choose a password with a length of one to eight characters, inclusive. Assume that 10,000 passwords can be tested per second. The system administrators want to expire passwords once they have a probability of 0.10 of having been guessed. Determine the expected time to meet this probability under each of the following conditions. (a) Password characters may be any ASCII characters from 1 to 127 , inclusive. (b) Password characters may be any alphanumeric characters ( "A" through "Z", "a" through " z ", and " 0 " through " 9 "). (c) Password characters must be digits