If A and B are independent, then [tex]P(A\cap B)=P(A)\cdot P(B)[/tex].
We have:
[tex]P(A)=\dfrac{2}{3},\ P(A\cap B)=\dfrac{2}{9}[/tex]
Substitute:
[tex]\dfrac{2}{9}=\dfrac{2}{3}P(B)\qquad|\cdot3\\\\\dfrac{2}{3}=2P(B)\qquad|:2\\\\\dfrac{1}{3}=P(B)\\\\\boxed{P(B)=\dfrac{1}{3}}[/tex]