And so to gets the "volume"..we arrange the given quotient..
"volume of solution"="moles of solute"/"concentration"
a. And so if 3.0*mol are required from 12.0*mol*L^-1 HCl...we take the quotient...
(3.0*mol)/(12.0*mol*L^-1)=0.250*L (mind you I don't think you can get HCl at this concentration....)
b. And if 3.0*mol are required from 2.0*mol*L^-1 HCl...we take the quotient...
(3.0*mol)/(2.0*mol*L^-1)=1.50*L
c. And if 3.0*mol are required from 0.5*mol*L^-1 HCl...we take the quotient...
(3.0*mol)/(0.50*mol*L^-1)=6.0*L
d. And if 3.0*mol are required from 0.010*mol*L^-1 HCl...we take the quotient...
(3.0*mol)/(0.010*mol*L^-1)=300.0*L
And clearly this last is an impratical proposition....