for (b)

$$\left(a \bigcap b \right) = \left(a' \bigcup b' \right)$$

for problem 2 S is just S. You don't know what it is so just call it S. Your answer will include it.

use the above formula. use (1-p) for the probability of the complement

for the 2nd one just do what you did in 1c with different numbers and the unknown S.