Assume that you have 1 L of solution.
(a) 15 % w/v
#"Mass of NaCl" = 1000 color(red)(cancel(color(black)("mL solution"))) × "15 g NaCl"/(100 color(red)(cancel(color(black)("mL solution")))) = "150 g NaCl"#
(b) 15 % w/w
The density of a 15 % w/w NaCl solution is 1.1135 g/mL.
Thus, the mass of 1 L of this solution is
#1000 color(red)(cancel(color(black)("mL"))) × "1.1135 g"/(1 color(red)(cancel(color(black)("mL")))) = "1113.5 g"#
#"Mass of NaCl" = 1113.5 color(red)(cancel(color(black)("g solution"))) × "15 g NaCl"/(100 color(red)(cancel(color(black)("g solution")))) = "167 g NaCl"#
(c) 15 % v/v
This unit is usually used for solutions of liquids in liquids. However,
#"Volume of NaCl" = 1000 color(red)(cancel(color(black)("cm"^3 color(white)(l)"solution"))) × ("15 cm"^3 color(white)(l)"NaCl")/(100 color(red)(cancel(color(black)("cm"^3color(white)(l) "solution")))) =150 color(white)(l)"cm"^3 "NaCl"#
#"Mass of NaCl" = 150 color(red)(cancel(color(black)("cm"^3 color(white)(l)"NaCl"))) × "2.165 g NaCl"/(1color(red)(cancel(color(black)("cm"^3color(white)(l) "NaCl")))) = "325 g NaCl"#
