A woman complete a journey in 15 hours. She travels first half of the journey at the rate of 21 km/hr and second half at the rate of 24 km/hr. Find the total journey in km.  Choose the correct choice from the following choices
A) 336 km .
B) 216 km .
C) 314 km .
D) 224 km .
E) 544 km .

Rationale: "0.5 x / 21 + 0.5 x / 24 = 15 - - > x / 21 + x / 24 = 30 - - > x = 336 km . a"
Answer: A