To find this mass we will use the mass percent concentration formula, which is:
m/m% = mass of solute/mass of solution
We have the percentage already and the mass of the solute, now let's apply to our formula:
0.127 = 0.50/mass of solution, I am using 12.7/100 = 0.127, since it's percent
mass of solution = 3.9 grams, letter A