Question 1200128
First task could be, find the rate of all three machines working together.
<pre>
WHICH MACHINE          RATE, acres per hours
small                   100/24
medium                  100/18
large                   100/12
All-Together       100/24+100/18+100/12
</pre>


{{{(3/3)(100/24) + (4/4)(100/18) + (6/6)(100/12)}}}

{{{300/72+400/72+600/72}}}

{{{1300/72}}}

{{{325/18}}}--------the rate of three-combined machines


800 acres, how much time?

{{{(325/18)*x=800}}}


{{{x=800(18/325)}}}


44 hours 19 minutes