If a child walks at the rate of 5m/min from his home, he is 6 minutes late for school, if he walks at the rate of 7m/min he reaches half an hour earlier. How far is his school from his home ? Answers:
A) 450 min
B) 540 min
C) 630 min
D) 360 min
E) none of these

Rationale: let the distance between home and school is x . let actual time to reach be t . thus , x / 5 = t + 6 - - - - ( 1 ) and x / 7 = t - 30 - - - - - ( 2 ) solving equation 1 and 2 x = 630 min answer : c
Answer: C