<PRE><B>Question 1024963</B>
Add the different rates of printing
to get their rate printing together.
Let {{{ t }}} = time in hours to 
produce paper
{{{ 1/6 + 1/9 + 1/12 = 1/t }}}
Multiply both sides by {{{ 36t }}}
{{{ 6t + 4t + 3t = 36 }}}
{{{ 13t = 36 }}}
{{{ t = 2 + 10/36 }}}
Convert the fraction to minutes
{{{ ( 10/36 )*60 = 600/36 }}}
{{{ 600/36 = 16 + 2/3 }}}   min
Convert the fraction to seconds
{{{ ( 2/3 )*60 = 40 }}} sec
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Working together, the presses take
2 hrs 16 min 40 sec
--------------------
check:
{{{ 1/6 + 1/9 + 1/12 = 1/2.7692 }}}
{{{ .1667 + .1111 + .0833 = .3611 }}}
{{{ .3611 = .3611 }}}
OK</PRE>