Answer : The original concentration of HCl is 0.04 M
Explanation:

According to the neutralization law,
where,
= molarity of NaOH solution = 0.100 M
= volume of NaOH solution = 60.0 ml
= molarity of HCl solution = ?
= volume of HCl solution = 150 ml
Now put all the given values in the above law, we get the molarity of HCl solution.
Therefore, the original concentration of HCl is 0.04 M