Question 1070250
Distance = rate x time
d = rt


Dennis 
rate = 4
time = t  {left at same time}
d = 4t   {distance = rate x time}


Chris
rate = 2
time = t   {left at same time}
d = 2t   {distance = rate x time}


Combined distances must be no more than 15 miles.


4t + 2t = 15   {added distances and set equal to 15}
6t = 15 {combined like terms}
t = 2.5 hours   {divided each side by 6}


.5 hours is 30 minutes.


They can talk for 2 hours and 30 minutes,
or 2.5 hours as requested for rounding.
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