Answer
See below.
Work Step by Step
a) In this case the events are independent, both having probability $\frac{4}{52}$, thus the probability is: $\frac{4}{52}\frac{4}{52}=\frac{1}{169}$
b) In this case the events are not independent. The first one has probability $\frac{4}{52}$, and the second one has probability $\frac{3}{51}$. Thus the probability is: $\frac{4}{52}\frac{3}{51}=\frac{1}{221}$
