Question 769182
25% salt solution?  Not likely.  Ignoring that,


All in variables:
w = pints of water to add, UNKNOWN
c = concentration as percent of available salt solution, 25%
v = pints of the available salt solution to start, 16 pint
f = the concentration of salt wanted, when finished, 20%


Equation:
{{{highlight(vc/(v+w)=f)}}}
Solve for w.