`A` & `B` are two events such that `P(A \cup B) = 4/5`, `P(\bar{A} \cup \bar{B}) = 7/10` and `P(B) = 2/5`, then value of `P(A)` is --
(a) `9/10`, (b) `7/10`, (c) `3/5`, (d) `8/10`