By using the digits 0, 1, 2, 3, 4 and 5 John arranges the number in ascending order as follow:
0, 1, 2, 3, 4, 5, 10, 11, 12, 13, 14, 15, 20, 21, 22, 23, 24, 25, 30, 31, ….



(a) How many of the 10-digit numbers have exactly three 4s?
(b) What is the number of the 99999th term?