Please Answer them all for an upvote and helpful ratings. Thank you. Show your formula and solutions to the following problems:

11. There are 10 men attending a directors meeting, how many handshakes were exchanged between the men? 12. A lock contains 5 digits in its code. How many codes can be formed if there are no restrictions? 13. A witness to a hit and run accident told the police that the license number contained the letters RLH followed by 3 digits, the first of which is a 5. If the witness cannot recall the last 2 digits, but is certain that all 3 digits are different, find the maximum number of automobile registrations that the police may have to check. 14. Leo, Ric, Mark, and Niko are going to play golf. They will randomly select teams of two players each. a. How many team combinations are possible? b. List them. 15. A movie theater sells 3 sizes of popcorn (small, medium, and large) with 3 choices of toppings (no butter, butter, extra butter). How many possible ways can a bag of popcorn be purchased?16. Concerning a car license plate in the Philippines (3 letters and 3 numbers). How many plates can be formed if the first and last letter are different? 17. There are 2 major roads from city X to city Y and 4 major roads from city Y to city Z. How many different trips can be made from city X to city Z passing through city Y? 18. There are 12 distinct books composed of five Mathematics and four English and three Science books to be arranged in a shelf. In how many ways can these books be put in to a shelf if the same subjects must be put together? 19. A maintenance computer has 8 ports. At any given time each port is in use or not in use. How many of these entail the use of at least one port