[tex] \sqrt{9a} + \sqrt{25a} - \sqrt{49a} = \sqrt{ {3}^{2}a } + \sqrt{ {5}^{2} a} - \sqrt{ {7}^{2} a} = 3 \sqrt{a} + 5\sqrt{a} - 7\sqrt{a} = 8\sqrt{a} - 7\sqrt{a} = \sqrt{a}[/tex]

[tex] \sqrt{64b} - \frac{1}{6} \sqrt{36b} = \sqrt{ {8}^{2} b} - \frac{1}{6} \sqrt{ {6}^{2}b } = 8 \sqrt{b} - \frac{1}{6} \times 6 \sqrt{b} = 8 \sqrt{b} - \sqrt{b} = 7 \sqrt{b} [/tex]

[tex]2 \sqrt{0.04c} - 0.3 \sqrt{16c} + \frac{1}{3} \sqrt{0.81c} = 2 \sqrt{ {0.2}^{2}c } - 0.3 \sqrt{ {4}^{2} c} + \frac{1}{3} \sqrt{ {0.9}^{2} c} = 2 \times 0.2 \sqrt{c} - 0.3 \times 4 \sqrt{c} + \frac{1}{3} \times 0.9 \sqrt{c} = 0.4 \sqrt{c} - 1.2 \sqrt{c} + 0.3 \sqrt{c} = 0.7 \sqrt{c} - 1.2 \sqrt{c} = - 0.5 \sqrt{c} [/tex]

[tex]0.4 \sqrt{100m} + 15 \sqrt{ \frac{4}{9} m} - 1.2 \sqrt{2.25m} = 0.4 \sqrt{ {10}^{2}m } + 15 \sqrt{( \frac{2}{3} ) {}^{2} m} - 1.2 \sqrt{1.5 {}^{2} m} = 0.4 \times 10 \sqrt{m} + 15 \times \frac{2}{3} \sqrt{m} - 1.2 \times 1.5\sqrt{m} = 4\sqrt{m} + 10\sqrt{m} - 1.8\sqrt{m} = 14\sqrt{m} - 1.8\sqrt{m} = 12.2\sqrt{m} [/tex]