A walks around a circular field at the rate of one round per hour while B runs around it at the rate of six rounds per hour. They start at same point at 7:30 am. They shall first cross each other at ?  Options:
A) 7:15 am  B) 7:30 am  C) 7: 42 am  D) 7:50 am  E) 7:60 am
Explanation:   Relative speed between two = 6-1= 
<gadget id="calculator">6-1</gadget>
<output>5</output>
5 round per hour   They will cross when one round will complete with relative speed,   which is 1/5 hour= 12 mins.   So 7:30 + 12 mins = 7:42   Option 7: 42 am
<result>C</result>
A walks around a circular field at the rate of one round per hour while B runs around it at the rate of six rounds per hour. They start at same point at 7:30 am. They shall first cross each other at ?