please help this probability and statistics question with clear steps and also expatiation, thankkk so much

1. A mechanism may be set at any one of four positions, say a, b, c and d. There are 8 such mechanisms which are inserted into a system.~ [a] In how many ways may this system be set? (4 marks) [b] Assume that these mechanisms are installed in some pre-assigned (linear) order. How many ways of setting the system are available if no two adjacent mechanisms are in the same position? (5 marks) [c] How many ways are available if only positions a and b are used and these are used equally often? (3 marks) [d] How many ways are available if only two different positions are used and one of these positions appears three times as often as the other? (6 marks)