Correct Answer: 50 km/hr

Solution : Average speed = $\frac{\text{Total Distance}}{\text{Total Time}}$
The person covers the first 35 km in 60 minutes and the next 40 km in 30 minutes.
Total Distance = 35 km + 40 km = 75 km
Total Time = 60 minutes + 30 minutes = 90 minutes = 1.5 hours
Average speed = $\frac{\text{Total Distance}}{\text{Total Time}}$ = $\frac{75}{1.5}$ = 50 km/hr
So, the average speed for the whole journey is 50 km/hr.
Hence, the correct answer is 50 km/hr.