Answer:
6.25 grams is the mass of solute dissolved.
Step-by-step explanation:
w/w % : The percentage mass or fraction of mass of the of solute present in total mass of the solution.

Mass of the solution = 50.0 g
Mass of the solvent = x
w/w % = 12.5%

x = 6.25 g
6.25 grams is the mass of solute dissolved.