prepare 500mM 100 ML HCL (37% purity, density 1.8)
Your question isn't stated very well. Do you mean something like this?
Prepare 100 mL of a 500 mM HCl solution using HCl with a purity of 37% HCl and a density of 1.18 g/mL.
If so, the first thing to do is to calculate the molarity of the 37% HCl solution.
That will be 1000 mL x 1.18 g/mL x 0.37 = ?? grams HCl in 1 L of solution.
Then moles = ??grams/molar mass HCl. That will be the molarity since that is the moles in 1 L soln.
Then the dilution formula is mL x M = mL x M. Post your work if you need additional assistance.