Correct Answer - Option 4 : 871 kms

**Given:**

Speed of goods train whose length is 1680 m and starts at 7 am = 48 km/hr

Speed of mail train whose length is 5320 m and starts at 12 noon = 67 km/hr

**Concept used:**

Relative speed when direction is same = Difference of both speeds

Distance = Speed × Time

**Calculation:**

Relative speed = (67 – 48) km/hr

⇒ 19 km/hr

Distance covered by goods train between 7 am to 12 noon (5 hours) = (48 × 5) km

⇒ 240 km

So, Total distance = 240 km + 1680 m + 5320 m

⇒ 240 km + 7 km = 247 km

Time taken by mail train to cross goods train = 247/19

⇒ 13 hours

Distance covered by mail train in 13 hours = (13 × 67) km

⇒ 871 km

**∴ The required distance is 871 km**