Determine the mass, in grams, of water contained in 0.25 litres of aqueous solution that has 10% dissolved salt and density equal to 1.10 g/cm3

What is the mass of the 250 cc solution. That's 1.10 g/cc x 250 cc = 275 grams.

10% NaCl means 10g NaCl/100 g solution. So how much NaCl is in 250 cc? That's 10 g x 250/100 = 25 g.
So 275 g total - 25 g salt = 250 g H2O. Check my work carefully.