JEE Main Physics question

A man walks on a straight road from his home to a market 2.5 km away with a speed of 5 km/h. Finding the market closed, he instantly turns and walks back home with a speed of 7.5 km/h. The average speed of the man over the interval of time 0 to 40 min is equal to [AMU (Med.) 2002]

• (A)5 km/h
• (B)25/4 km/h
• (C)30/4 km/h
• (D)45/8 km/hCorrect