Let A and B be two independent events such that $P(A) = \large\frac{1}{5} \: P( A \cup B ) = \large\frac{7}{10}$. Ten $P(\overline B)$ is equal to

Question

$\begin {array} {1 1} (A)\;\large\frac{3}{8} & \quad (B)\;\large\frac{2}{7} \\ (C)\;\large\frac{7}{9} & \quad (D)\;None\: of \: these \end {array}$