Let the speed of first car be x mph
the speed of the second one is (x+3) mph
Relative speed=x+x+3=(2x+3) mph
but
time=distance/speed
thus
3=(261)/(2x+3)
solving for x we get:
3(2x+3)=261
6x+9=261
6x=261-9
6x=252
hence:
x=42 mph
Thus the average speed of first car is 42 mph
Average speed of the second car is (42+3)=45 mph
