car A 90 kms per hour and sets off at 2.00
car B 100 kms per hour and sets off at 2.10.
At 2.10 the A car has done allready 15 kms.
relative speed between the two cars is 10 kms.
So it will take car B 1 hour and 30 to catch up to car A and cover the 15 kms.
In one and a hals hour car B has covers 150 km.
Car A 135 plus the 10 minuttes difference between the two starting hours that equals 15 kms and adds up to 150 for car A also.
So they will meet at 15.40 at 150 kms