[Thought Hammer]

This has stumped me for days and I was hoping someone could help me out.
Imagine the lab scenario with some arbitrary values:

You have a beaker with a measured 10mL of HCl (unknown Molarity) which you weigh the solution as 10g. You need to find out the mass of the solvent.

Ultimately, I need to determine the Molarity of the solution but I need the mass of solvent(the water in the HCl solution) to determine the mass of solute which will allow me to determine the moles of solute necessary for the Molarity.

10g_solution-g_solvent=_Y_g_solute
_Y_g_solute x 1 mol HCl/(1.008g+35.45g)=_X_mol HCl
_X_mol HCl solute/10mL HCl solution = Molarity of HCl solution

People have been telling me I need to have density to obtain the mass of solvent but I don't know how I'd get that.  

[Borek]

Something is missing here. What is the complete procedure to follow, or what are all the exact given data?

[enahs]

You have the density of the solution. You have 10 g in 10 mL, so your degnsity is just 10g/10mL = 1g/mL.

Without more information or a lot more significant figures, your answer is going to be VERY little HCl and mostly solvent; as the density is that of pure water as it stands with the number of sig figs and the data given.