Answer
$4$
Work Step by Step
Let $f(x)=\int_{0}^{4} \dfrac{1}{\sqrt {4-x}} dx$
Now, $\lim\limits_{k \to 4^{-}} f(x)= \lim\limits_{k \to 4^{-}} \int_{0}^{k} \dfrac{1}{\sqrt {(4-x)}} dx$
Thus, $\lim\limits_{k \to 4^{-}} [-2 \sqrt {(4-x)}]_{0}^{k}\lim\limits_{k \to 4^{-}} [-2 \sqrt {(4-k)}+4]= -2(0)+4=4$
