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, for the first one has probability $\frac{4}{52}$, and the second one has probability $\frac{4}{51}$. Thus the probability is: $\frac{4}{52}\frac{4}{51}=\frac{4}{663}$
