Add 2x to both sides,
3x+9=18
Subtract 9 from both sides. 3x=9
Divide both sides by 3.
x=3
Initial = 50lbs
1st 6 hours =100
2nd 6 hours = 200
3rd 6 hours = 400
After 18 hours it will be 750 pounds
We must find a pattern in the powers of 3:





So, as you can see, both
and
end with 1. So, we can generalize as follows:




Since
, we can deduce that
ends with 9.
Answer:
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