Two events $A$ and $B$ are mutually independent and
$$\mathrm { P } ( A ) = \frac { 2 } { 3 } , \quad \mathrm { P } ( A \cup B ) = \frac { 5 } { 6 }$$
What is the value of $\mathrm { P } ( B )$? [3 points]\\
(1) $\frac { 1 } { 3 }$\\
(2) $\frac { 5 } { 12 }$\\
(3) $\frac { 1 } { 2 }$\\
(4) $\frac { 7 } { 12 }$\\
(5) $\frac { 2 } { 3 }$