If A and B are two events such that $P(B)=\frac{3}{5},P(A|B)=\frac{1}{2}$ and $P(A ∪ B)=\frac{4}{5}$, then P(A) is equal to :

$\frac{3}{10}$ $\frac{1}{5}$ $\frac{1}{2}$ $\frac{1}{3}$

$\frac{1}{2}$