Question 719867
Think of this as 1 car standing still and
the other car traveling at the sum of their speeds
Let {{{ s }}} = the speed of the slower car
{{{ s + 15 }}} = the speed of the faster car
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{{{ 405 = ( s + s + 15 )*3 }}}
{{{ 405 = 6s + 45 }}}
{{{ 6s = 360 }}}
{{{ s = 60 }}}
{{{ s + 15 = 75 }}}
The speeds of the cars are 60 mi/hr and 75 mi/hr