Car X began traveling at an average speed of 35 miles per hour. After 84 minutes, car Y began traveling at an average speed of 42 miles per hour. When both cars had traveled the same distance, both cars stopped. How many miles did car X travel from the time car Y began traveling until both cars stopped?	Choose the correct answer.
A) 140
B) 175
C) 210
D) 245
E) 270

Rationale: in 84 minutes , car x travels 49 miles . car y gains 7 miles each hour , so it takes 7 hours to catch car x . in 7 hours , car x travels 245 miles . the answer is d .
Answer: D