1. Write the balanced chemical equation:

HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)

2. Determine the moles of NaOH used:

Molarity (M) = moles (mol) / volume (L)

moles NaOH = Molarity * volume

moles NaOH = 6.90 M * 0.0164 L = 0.113 mol

3. Use the stoichiometry of the balanced equation to find moles of HCl:

The balanced equation shows a 1:1 mole ratio between HCl and NaOH. This means that 0.113 moles of NaOH reacted with 0.113 moles of HCl.

4. Calculate the concentration of the HCl solution:

Molarity (M) = moles (mol) / volume (L)

Molarity HCl = 0.113 mol / 0.300 L = 0.377 M

Therefore, the concentration of the HCl solution is 0.377 M.