Correct Answer - Option 5 : 12 seconds

**Given:**

Length of first train = 100 m

Length of second train = 140 m

Speed of first train = S1 = 29 km/hr

Speed of second train = S2 = 43 km/hr

**Formula:**

If trains are running in the opposite direction then,

Relative speed = S1 + S2

Crossing time = total length of train/relative speed

**Calculations:**

Relative speed = (29 + 43) kmph = 72 kmph

⇒ 72 × (5/18)

⇒ 20 m/sec

Required time = total length of train/relative speed

⇒ (100 + 140)/20 = 12

⇒ 12 seconds

**∴**** Both trains crosses each other after 12 sec.**