Two trains of length 120 m and 280 m are running towards each other on parallel lines at 42 kmph and 30 kmph respectively. In what time will they be clear of each other from the moment they meet? Select the correct option.
A) 10 sec  B) 30 sec  C) 40 sec  D) 20 sec  E) 50 sec
D   Relative speed = (42 + 30) * 5/18 = 4 * 5= 
<gadget id="calculator">4 * 5</gadget>
<output>20</output>
20 mps.   Distance covered in passing each other= 120 + 280= 
<gadget id="calculator">120 + 280</gadget>
<output>400</output>
400 m.   The time required= d/s = 400/20= 
<gadget id="calculator">400/20</gadget>
<output>20</output>
20 sec.
<result>D</result>
Two trains of length 120 m and 280 m are running towards each other on parallel lines at 42 kmph and 30 kmph respectively. In what time will they be clear of each other from the moment they meet?