In how many of the passwords of Exercise 15 (a) are the first three digits even?...

In how many of the passwords of Exercise 15

(a) are the first three digits even?

(b) are the three even digits consecutive?

(c) are the four odd digits consecutive?

(d) are no two odd digits consecutive?

Reference:

Find the number of passwords that use each of the digits 3, 4, 5, 6, 7, 8, 9 exactly once.