Average speed of car 1 = 45 mph. average speed of car 2 = 65 mph. time elapsed between start of car 1 and start of car 2 = 18 minutes. how long until the cars lapse

I'm assuming the two cars start from the same point! 

Let's measure time t from the time when Car 2 starts. 

Then the distances travelled by the cars up to the time of overtaking, t, must be the same. 

And we need to measure all time in hours, so 18 mins. is 0.3 hours. 

So, 45 x (0.3 + t) = 65 x t, so 20t = 13.5, so t = 13.5/20 = 27/40 = 40.5/60, i.e. 40 min 30 sec

You didn’t put the necessary image to solve the question : p

Doesn't make sense try again