Answer : The original concentration of the acid solution is 0.869 M
Explanation :
To calculate the concentration of acid, we use the equation given by neutralization reaction:

where,
are the n-factor, molarity and volume of acid which is

are the n-factor, molarity and volume of base which is NaOH.
We are given:

Putting values in above equation, we get:

Therefore, the original concentration of the acid solution is 0.869 M