A passenger sitting in a train $A$ moving at $90 \mathrm {~km} \mathrm {~h} ^ { - 1 }$ observes another train $B$ moving in the opposite direction for 8 s . If the velocity of the train $B$ is $54 \mathrm {~km} \mathrm {~h} ^ { - 1 }$, then length of train $B$ is:\\
(1) 120 m\\
(2) 320 m\\
(3) 80 m\\
(4) 200 m