Question 1200306
This kind has been done so many, many times.



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928 kilometers apart at the same time and travel toward each other. One bus travels 12 km/h slower than the other. If they meet in 4 hours, 
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D kilometers apart at the same time and travel toward each other. One  travels K km/h slower than the other. If they meet in T hours, 
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{{{highlight_green((r+(r-K))T=D)}}}
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{{{2r-K=D/T}}}
{{{2r=D/T+K}}}

{{{r=D/(2T)+K/2}}}

{{{r=D/(2T)(+KT)/(2T)}}}

{{{highlight_green(r=(D+KT)/(2T))}}}