Question 945183
Let {{{ d }}} = the distance in meters the faster runner travels
until the slower runner is caught
Let {{{ t }}} = time in seconds for faster runner to
catch slower runner
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faster runner's equation:
{{{ d = 8t }}}
slower runner's equation:
{{{ d - 81 = 2t }}}
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By substitution:
{{{ 8t - 81 = 2t }}}
{{{ 6t = 81 }}}
{{{ t = 13.5 }}} 
In 13.5 seconds the faster runner catches
the slower runner