A man walks on a straight road from his home to a market 2.5 km away with speed of 5 `\frac { k m } { h \r }`. Finding the market closed, he instantly turns and walks back home with a speed of 7.5 `\frac { k m } { h \r }`. The average speed of the man over the interval of time 0 to 40 min is equal to

Options

A. 5 `\frac { k m } { h \r }`
B. `\frac { 25 } { \4 }` `\frac { k m } { h \r }`
C. `\frac { 30 } { \4 }` `\frac { k m } { h \r }`
D. `\frac { 45 } { \8 }` `\frac { k m } { h \r }`

Answer

D