When preparing diluted solutions from concentrated solutions , we can use the following equation;
c1v1 =c2v2
Where c1 and v1 are the concentration and volume of the concentrated solution
c2 is the concentration of the diluted solution to be prepared
v2 is the volume of the diluted solution
Substituting the values;
12.0 M x v1 = 0.339 M x 100 mL
v1 = 2.825 mL needs to be taken from the stock solution