physics
posted by Anonymous .
How long does it take an automobile traveling in the left lane at 60.0 km/h to overtake (become even with) another car that is traveling in the right lane at 40.0 km/h when the carsâ€™ front bumpers are initially 100 m apart?

Simplify the question. How long does it take a car traveling at 60 km/h to travel 100 m?

9s

3.6s!

nevermind, the previous one is correct. how would I go on about that?

I don't think either of your responses is correct. I don't think my hint is correct, either.
distance = rate x time
distance traveled by 40 km/hr car is
d = 40t. solve for t = d/40
distance traveled by 60 km/hr car is
d + 100 = 60t. solve for t = (d+100)/60
The times are equal. Set them equal to each other and solve for distance, then solve for time it takes for the car traveling at 60 km/h to travel d + 100. 
Aren't you suppose to convert km to m (since the distance is in m)?

Yes, you may convert 100 m to 0.1 km in which case d will be in km or you may convert 40 km/h and 60 km/h to m/h and d is then in meters. However, since both 40 km/h and 60 km/h are on opposite sides of the equation, the conversion factor cancels and what I set up above gives the same answer with or without the conversion. Probably the math people won't like that because it isn't good math and I recommend the conversions.