The mass of 15.0 % (m/m) NaOH solution that contains 125 g NaOH is 833.33 g
calculation
m/m% = mass of solute/ mass of solvent x 100
M/M% = 15.0% into fraction= 15/100
mass of solute (NaOH) = 125 g
let the mass of solvent ( NaOH solution) be represented by Y
Therefore 15/100 = 125/Y
by cross multiplication
=15 x Y =125 x 100
15 y = 12500
divide both side by 15
y =833.33 g