\begin{questions}
\item $\begin{aligned}[t]
C&= \sqrt{27}-2\sqrt{75}+3\sqrt{12}\\
&= 3\sqrt{3}-2\times5\sqrt{3}+3\times2\sqrt{3}\\
&= (3-10+6)\sqrt{3}\\
&= -\sqrt{3}.
\end{aligned}$

\item $\begin{aligned}[t]
D&= \sqrt{\frac{6,3}{2,8}}\times\sqrt{\frac{18}{0,72}}\\
&= \sqrt{\frac{63}{28}}\times\sqrt{\frac{18\times 100}{72}}\\
&=\sqrt{\frac{9}{4}}\times \sqrt{\frac{100}{4}}\\
&= \sqrt{\frac{9}{4}}\times \sqrt{25}\\
&= \frac{3}{2}\times 5\\
&= \frac{15}{2}.
\end{aligned}$
\end{questions}
