Answer the questions below. (a) An experiment involves 30 participants. From these, a group of 5 participants is to be tested under a special condition. How many groups of 5 participants are possible? (b) To log on to a certain computer account, the user must type in a 4-letter password. In such a password, no letter may be repeated, and only the lower case of a letter may be used. How many such 4-letter passwords are possible? (There are 26 letters in the alphabet.)