$\sqrt{9a} + \sqrt{25a} - \sqrt{49a} = \sqrt{9} * \sqrt{a} + \sqrt{25} * \sqrt{a} - \sqrt{49} * \sqrt{a} = 3\sqrt{a} + 5\sqrt{a} - 7\sqrt{a} = \sqrt{a}(3 + 5 - 7) = \sqrt{a}$

$\sqrt{64b} - \frac{1}{6}\sqrt{36b} = \sqrt{64} * \sqrt{b} - \frac{1}{6} * \sqrt{36} * \sqrt{b} = 8\sqrt{b} - \frac{1}{6} * 6 * \sqrt{b} = 8\sqrt{b} - \sqrt{b} = \sqrt{b}(8 - 1) = 7\sqrt{b}$

$2\sqrt{0,04c} - 0,3\sqrt{16c} + \frac{1}{3}\sqrt{0,81c} = 2 * \sqrt{0,04} * \sqrt{c} - 0,3 * \sqrt{16} * \sqrt{c} + \frac{1}{3} * \sqrt{0,81} * \sqrt{c} = 2 * 0,2 * \sqrt{c} - 0,3 * 4 * \sqrt{c} + \frac{1}{3} * 0,9 * \sqrt{c} = 0,4\sqrt{c} - 1,2\sqrt{c} + 0,3\sqrt{c} = \sqrt{c}(0,4 - 1,2 + 0,3) = -0,5\sqrt{c}$

$0,4\sqrt{100m} + 15\sqrt{\frac{4}{9}m} - 1,2\sqrt{2,25m} = 0,4 * \sqrt{100} * \sqrt{m} + 15 * \sqrt{\frac{4}{9}} * \sqrt{m} - 1,2 * \sqrt{2,25} * \sqrt{m} = 0,4 * 10 * \sqrt{m} + 15 * \frac{2}{3} * \sqrt{m} - 1,2 * 1,5 * \sqrt{m} = 4\sqrt{m} + 5 * 2\sqrt{m} - 1,8\sqrt{m} = 4\sqrt{m} + 10\sqrt{m} - 1,8\sqrt{m} = \sqrt{m}(4 + 10 - 1,8) = 12,2\sqrt{m}$