What we are give: Concentration of base (CB) = 3.4 × [tex] 10^{-3} [/tex]
Then convert all volume in ml to L.
Volume of base (VB) 25.0ml = 0.025L
Volume of acid (VA) 16.6ml = 0.0166L
Now that we have everything we use the formula CAVA=CBVB.
Make 'CA' the subject then solve.
CA=[tex] \frac{CBVB}{VA} [/tex]