Explain how you woud make 200.0 g of a .900 percent by mass solution of salt
(NaCl in water)
0.9% w/w NaCl in water means 0.9g NaCl/100 g solution.
So you put 0.9 g NaCl in 99.1g H2O and shake till dissolved. You want to make 200 g of this so double those numbers.