First we multiply by the conjugate:
We now multiply top and bottom by 
(since we're interested in the
limit as 
, we don't need to worry about the sign of x - assume
that we've gone to the positive side of zero):
We can now evaluate the limit as the limit of the numerator over the limit of the denominator, and so we get
a) The concentration of salt after t minutes is given by the amount of salt (as grams of salt as a function of time) over the volume of the water (again, as a function of time). Hence, we write
b)
That is, eventually, the freshwater is ``overwhelmed'' by the salt water, and the concentration tends to that of the concentration of the brine.