Train $A$ and train $B$ are running on parallel tracks in the opposite directions with speeds of $36 \mathrm{~km} / \mathrm{hour}$ and $72 \mathrm{~km} / \mathrm{hour}$, respectively. A person is walking in train A in the direction opposite to its motion with a speed of $1.8 \mathrm{~km} /$ hour. Speed (in $\mathrm{ms}^{-1}$ ) of this person as observed from train B will be close to : (take the distance between the tracks as negligible)