<PRE><B>Question 82938</B>
Let x=time it takes for 6 tractors to plow the field.

Each tractor can plow the field at the rate of 1/4 of field per 12 hours. Or one tractor can plow the field(4/4)in 4*12=48 hours.  In other words, it takes 48 tractor-hours to plow the field.

So x=(Number of Tractor-Hours Required)/(Number of Tractors)-- in this case -6

1 tractor takes 48/1=48 hours
2 tractors takes 48/2=24 hours
3 tractors takes 48/3=16 hours
4 tractors takes 48/4=12 hours
6 tractors takes 48/6=8 hours-------------------------ans

Hope this helps----ptaylor</PRE>