(a)
$P(A) = 0.25,\ P(B) = 0.50,\ P(A \cap B) = 0.14$
$P(A \cup B) = P(A) + P(B) - P(A \cap B)$
$= 0.25 + 0.50 - 0.14 = 0.61$
$\therefore P\left( \overline{A} \cap \overline{B} \right) = P(\overline{A \cup B})$=$1 - \ P(A \cup B)$
$= 1 - 0.61 = 0.39$