Correct Answer - Option 1 :

18 min
**Given:**

Speed of thief = 9 km/h

Speed of policeman = 12 km/h

**Formula Used:**

Speed = Distance/Time

**Concept Used:**

If two objects are moving in the same direction with speeds S_{1} and S_{2},

Their relative speed is S_{1} – S_{2}

**Calculation: **

Only the thief runs for 6 minutes.

Distance covered by the thief = 9 × 5/18 × 6 × 60 m = 900 m

Relative speed = 12 – 9 = 3 km/h

⇒ 3 × 5/18 m/s

⇒ 5/6 m/s

Time to catch the thief = Time required to cover 900 = 900/(5/6) s

⇒ 900/5 × 6 s

⇒ 180 × 6 s

⇒ (180 × 6)/60 = 18 min

**∴ ****The p****oliceman will catch the thief in 18 min.**