posted by Chris .
How many grams of NaC2H3O2 (M=82.034 g mol-1) should be dissolved in 400 g of water to prepare a solution which is 11.28% NaC2H3O2 by mass?
[Mass of salt/(mass salt + 400)]*100 = 11.28
Solve for mass salt. The easiest way is to let mass salt = x where ever mass salt appears and solve for x.
I obtained an answer close to 50 grams. Post your work if you get stuck.