Question 986605
Let {{{ s }}} = the speed of Adam's bus
{{{ s - 20 }}} = the speed of Mike's bus
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The best way to solve this is to think of one 
of the buses standing still and the other one
traveling at the sum of their speeds.
It doesn't matter which one is standing still
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{{{ 270 = ( s + s - 20 )*3 }}}
{{{ 270 = ( 2s - 20 )*3 }}}
{{{ 270 = 6s - 60 }}}
{{{ 6s = 330 }}} 
{{{ s = 55 }}}
and
{{{ s - 20 = 35 }}}
The speed of Adam's bus is 55 mi/hr
The speed of Mike's bus is 35 mi/hr
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check:
{{{ d[1] = 55*3 }}}
{{{ d[1] = 165 }}} mi
and
{{{ d[2] = 35*3 }}}
{{{ d[2] = 105 }}} mi
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{{{ d[1] + d[2] = 165 + 105 }}}
{{{ d[1] + d[2] = 270 }}} mi
OK