Correct Answer - Option 4 : 14 km

**Given:**

S_{1} = 3 Km/h

S_{2} = 4 Km/h

Time difference in hour = (40 + 30)/60 = 7/6 hour

**Formula used:**

Distance = S_{1} × S_{2} × Time difference / Speed difference

**Calculation:**

Distance = (3 × 4 × 7/6)/1 = 14 Km

**∴ The distance between house and office is 14 Km.**

__ALTERNATE METHOD__

Let the total distance be x km

We know time = distance/speed,

Time taken to travel at 3 km/hour = x/3 hour and,

Time taken to travel at 4 km/hour = x/4 hour.

Total difference in time = 40 minutes + 30 minutes = 70 minutes or 70/60 hours.

⇒ x/3 – x/4 = 70/60

⇒ x/12 = 7/6

⇒ x = 14

∴ The distance between house and office is 14 Km.