\(\sqrt{28} + \sqrt{112} - \sqrt{k} = \sqrt{175}\) \(\sqrt{4 \times 7} + \sqrt{16 \times 7} - \sqrt{k} = \sqrt{25 \times 7}\) \(2\sqrt{7} + 4\sqrt{7} - \sqrt{k} = 5\sqrt{7}\) \(6\sqrt{7} - 5\sqrt{7} = \sqrt{k}\) \(\sqrt{k} = \sqrt{7}\) \(\implies k = 7\)