Answer: 0.42 M
Step-by-step explanation:

The expression used will be :
where,
= basicity of
= 1
= acidity of
= 2
= concentration of
= ?
= concentration of
= 0.45 M
= volume of
= 38.5 ml
= volume of
= 18.2 ml
Now put all the given values in the above law, we get the concentration:
By solving the terms, we get :
Therefore, the concentration of
is 0.42M