A train overtakes two girls who are walking in the opposite direction in which the train is going at the rate of 3 km/h and 6km/h and passes them completely in 36 seconds and 30 seconds respectively. The length of the train is:

Let the length of the train e x meter, and let the speed of train be y km/h, then

$x=y+3\times \frac{5}{18}\times 36$   --------(1)   and   

$x=y+6\times \frac{5}{18}\times 30$  ---------(2)

From eq (1) and (2), we get      

y = 12 km/h

Therefore,   $x=(y+3)\times \frac{5}{18}\times 36$   =>  x= 150 m