Question 886219
The above ans of Stan H is wrong.
Let x be the number of days.
Rate for each factory
1/4 plane per day
 1/5 plane per day
 1/7 plane per day
Therefore,
(1/4)x+(1/5)x+(1/7)x=83
multiply by 140 to get
35x+28x+20x=83*140
=>63x=11620
=>x=184.444 days