Distance between 2 villages A and B is 165km.a scooter rider starts from A to B at 75km at speed of 320km/hr.at the same time another scooter rider starts from B towards A at speed of 25km/hr.find when they will cross each other? ( 10 am)?

In your question, 75 km doesn't make sense/looks like a typo. Was this supposed to be a starting time instead? The solution below ignores it.

Let C be the point at which the scooters meet.
Let x be the distance from A to C, in km.
Then 165-x is the distance from B to C, in km.

Also, recall that time = distance/speed

Scooter A:
Time to get to meeting point = x km / 320 km/h
Scooter B:
Time to get to meeting point = (165-x) km / 25 km/h
Since they start out at the same time, these two times are equal:
x km / 320 km/h = (165-x) km / 25 km/h
25x = -320x + 52800
345x = 52800
x ~ 153 km
Sub 153 km back into either the Scooter A or Scooter B equation, for x, and solve for time, in hours.