Answer
$$2\sqrt{t+12 }+C$$
Work Step by Step
Given $$ \int \frac{d t}{\sqrt{t+12}}$$ Let $$ u^2= t+12\ \ \ \Rightarrow\ \ du= dt$$ Then \begin{align*} \int \frac{d t}{\sqrt{t+12}}&= \int \frac{2ud u}{u} \\ &=2u+c\\ &= 2\sqrt{t+12 }+C \end{align*}