A train leaves station X at 5 a.m. and reaches station Y at 9 a.m. Another train leaves station Y at 7 a.m. and reaches station X at 10 : 30 a.m. At what time do the two trains cross each other ?	Choose the correct choice.
A) 7 : 36 am
B) 7 : 56 am
C) 8 : 36 am
D) 8 : 56 am
E) None of these
Let the distance between X and Y be x km. Then,   the speed of A is x⁄4 km/h and that of B is 2x⁄7 km/h.   Relative speeds of the trains   = (x⁄4 + 2x⁄7) = 15x⁄28 km/h   Therefore the distance between the trains at 7 a.m.   = x - x⁄2 = x⁄2 km   Hence, time taken to cross each other   = x/2 /15x/28=x/2×28/15x=14/15×60=56min.   Thus, both of them meet at 7 : 56 a.m.   Answer 7 : 56 am
<result>B</result>
A train leaves station X at 5 a.m. and reaches station Y at 9 a.m. Another train leaves station Y at 7 a.m. and reaches station X at 10 : 30 a.m. At what time do the two trains cross each other ?