Question 1092475
<pre>
They are separating at the rate of 450+550 = 1000 mi/h.

We use the formula {{{D=RT}}} with D = 4000 mi and R = 1000 mi/h
                   {{{4000=1000T}}}
                   {{{4000/1000=1000T/1000}}}
                   {{{4=T}}}

answer: 4 hours.

Edwin</pre>