Question 496998
It would be the same if one car was not moving at all
and the other were traveling at their combined speed.

Let the two speeds be {{{s}}} and {{{s+9}}}

{{{(2s + 9)*3 = 405 }}}

{{{(2s + 9)= 405 /3 }}}

{{{2s + 9= 135 }}}

{{{2s = 135-9}}}

{{{2s = 126}}}

{{{s = 126/2}}}

{{{s = 63mph}}}


{{{s+9 = 72mph}}}

First car travels {{{189 miles}}}.
Second car travels {{{216 miles}}}.
Total {{{405miles}}}.