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

\(-3 \sqrt{112} = -3 ⋅ \sqrt{16} ⋅ \sqrt{7} = -3 ⋅ 4 ⋅ \sqrt{7} = -12 \sqrt{7} \text{.}\)

\(\sqrt{\frac{16}{49}} = {\sqrt{16} \over \sqrt{49}} = \frac{4}{7} \text{.}\)

\({45 \sqrt{400} \over 5 \sqrt{10}} = {45 \over 5} ⋅ {\sqrt{400} \over \sqrt{10}} = 9 \sqrt{40} = 9 ⋅ \sqrt{4} ⋅ \sqrt{10} = 9 ⋅ 2 ⋅ \sqrt{10} = 18 \sqrt{10}\)