This question was previously asked in

Bihar CET B.Ed. Official Paper Maths & Science (Held on 17 Oct 2015)

Option 3 : 5 km

In the below diagram shortest distance between starting point and destination denoted by point I and P respectively.

Given:

Distance IR = 6 km

Distance IO = 3 km

Distance PQ = 9 km

Distance PO = 4 km

Now, Triangle "POI" is a right-angled triangle, so using Pythagoras Theorem:

**PI2 = PO2 + IO2 **

**PI2 = (4)2 + (3)2**

**PI2 = 16 + 9**

**PI2 = 25**

**PI = √25**

**PI = 5**

Hence, the correct answer is "5 km".