Answer : The volume of 6 M HCl needed is, 10 mL
Explanation :
Formula used :

where,
are the initial molarity and volume of diluted HCl.
are the final molarity and volume of HCl.
We are given:

Now put all the given values in above equation, we get:

Hence, the volume of 6 M HCl needed is, 10 mL