Question 777206
I know what you mean, but first, be aware, you need to know in which directions each of these two cars are going.  If they are going in opposite directions, then state this.  


Now, assuming that you mean, the cars are traveling in opposite directions, away from eachother:

They travel for some time, h hours.

{{{35*h+50*h=400}}}
{{{(35+50)h=400}}}
{{{h=400/85}}}
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h is 4 hours 42 minutes...
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