Answer
Please see the work below.
Work Step by Step
We are given that
$[HCl]=1.4\times 10^{-3}M$
We know that
$[H^+]\times [OH^-]=1\times 10^{-14}$
Thus $OH^-=\frac{1\times 10^{-14}}{H^+}=\frac{1\times 10^{-14}}{1.4\times 10^{-3}}=7.14\times 10^{-10}$