Question 701606
(salt)/(salt solution)=0.40


The salt material is 100% salt.  The current solution is the lower concentration material at 28% or 0.28.  You have 40 grams of this solution and you do not need to know how much resulting solution quantity.

m= grams of salt solid to add,


{{{(m*1.00+40*0.28)/(m+40)=0.40}}}


Solve for m.