\(\sqrt{28}=\sqrt{4}⋅\sqrt{7}=2\sqrt{7}\text{.}\)

\(-7\sqrt{12}=-7⋅\sqrt{4}⋅\sqrt{3}=-7⋅2⋅\sqrt{3}=-14\sqrt{3}\text{.}\)

\(\sqrt{1\frac{13}{36}}=\sqrt{\frac{49}{36}}={\sqrt{49} \over \sqrt{36}}=\frac{7}{6}=1\frac{1}{6}\text{.}\)

\(\sqrt{11\frac{1}{4}}=\sqrt{\frac{45}{4}}={\sqrt{45} \over \sqrt{4}}={\sqrt{45} \over 2}=\frac{1}{2}\sqrt{45}=\frac{1}{2}⋅3⋅\sqrt{5}=1\frac{1}{2}\sqrt{5}\text{.}\)