If John covers a certain distance in 1 hr. 24 min. by covering two third of the distance at 4 kmph and the rest at 5 kmph, then find the total distance.  Choose the correct choice from the following choices
A) 9 km B) 2 km C) 1 km D) 6 km E) 7 km

Rationale: "explanation : let the total distance be y km . then , ( 2 / 3 ) y / 4 + ( 1 / 3 ) y / 5 = 7 / 5 y / 6 + y / 15 = 7 / 5 7 y = 42 y = 6 km answer : d"
Answer: D