<PRE><B>Question 1110573</B>
the salt enters the tank at rate:
R_in = (4gal/min)(4lbs/gal) = 16lbs/min
Since the tank loses liquid at a rate of 2gal/min:
4gal/min - 2gal/min = 2gal/min
after t minutes the number of gallons of brine in the tank is:
30 + 2t gallons 
after 10 minutes:
30 + 2(10) = 50 gallons
and
50(4) = 200lbs of salt
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170/4 = 42.5gallons of brine
42.5-30 = 12.5 gallons of brine need to be added
12.5/2 = 6.25 minutes to get 170lbs of salt in the tank
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I think this is what you were looking for. 
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