Question 333545
You need to understand the relationship:
d=r*t (distance = rate*time)
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Kim's distance after t hours:  {{{d[k]=40*t}}}
Jason's distance after t hours:  {{{d[j]=30*t}}}
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They are travelling in opposite directions and you need to know the time when they are 210 miles apart, so add their distances
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{{{210 = d[k]+d[j]=40*t + 30*t }}}
{{{210=70*t}}}
210/70 =t
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t = 3 hours