For part (b)
you can simplify further
the requirement is for a number to be less than 100, both numbers must be of 1, 2, 3, 4, 5...9 = 9 possible numbers that will do.
For part (c):
One can pick 3,4 as the leading digit:
2/10
One can pick 10,11,...20 (11 possible numbers)
=2/10*11/20
=22/200...