Two cyclist start on a circular track from a given point but in opposite direction with speeds of 7m/s and 8m/s. If the circumference of the circle is 630meters, after what time will they meet at the starting point?	Select
A) 20 sec B) 15 sec C) 42 sec D) 50 sec E) 1 min

Rationale: "they meet every 630 / 7 + 8 = 42 sec answer is c"
Answer: C