Correct Answer: Option B

Explanation

Let the distance from P to Q = d km  
(We don't need the actual value of d — it will cancel out.)

Time taken from P to Q = \(\frac{\text{d}}{90}\) hours  
Time taken from Q to P = \(\frac{\text{d}}{45}\) hours

Total distance travelled = d + d = 2d km  
Total time taken = \(\frac{\text{d}}{90}\)  + \(\frac{\text{d}}{45}\)

= \(\frac{\text{d}}{90}\)  + \(\frac{2d}{90}\) = \(\frac{3d}{90}\) 
= \(\frac{\text{d}}{30}\) hours  

Average speed = \(\frac{\text{total distance}}{\text{total time}}\)  
= 2d ÷ (\(\frac{\text{d}}{30}\))  = 2d × (\(\frac{30}{\text{d}}\)) = 60 km/h

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