Question 744989
Think of one train as standing still and the 
other approaching at the sum of their speeds
( it doesn't matter which train is moving )
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Let {{{ s }}} = the speed of the slower train
{{{ 2s }}} = the speed of the faster train
The time the moving train is traveling is
10 AM minus 6 AM = {{{ 4 }}} hrs
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{{{ 360 = ( s + 2s )*4 }}}
{{{ 360 = 12s }}}
{{{ s = 30 }}}
{{{ 2s = 60 }}}
The average speed of the freight train is 30 mi/hr
The average speed of the passenger train is 60 mi/hr
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check:
freight train:
{{{ d[1] = 30*4 }}}
{{{ d[1] = 120 }}}
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passenger train:
{{{ d[2] = 60*4 }}}
{{{ d[2] = 240 }}}
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{{{ d[1] + d[2] = 120 + 240 }}}
{{{ d[1] + d[2] = 360 }}} mi
OK