Correct Answer - Option 2 : 102 km

**Given:**

Initial speed of bus = 21 km/hr

Speed increases by 3 km/hr every hour

Time = 4 hours

**Calculation:**

Speed in 1^{st} hour = 21 km/hr

Speed in 2^{nd} hour = 24 km/hr

Speed in 3^{rd} hour = 27 km/hr

Speed in 4^{th} hour = 30 km/hr

Total distance covered in 4 hours = (21 + 24 + 27 + 30) km

**∴ Total distance traveled by bus in 4 hours is 102 km**