a)
$A = \sqrt{12} - \sqrt{3} + 2\sqrt{27} - \sqrt{48}$
$= \sqrt{4.3} - \sqrt{3} + 2\sqrt{9.3} - \sqrt{16.3}$
$= 2\sqrt{3} - \sqrt{3} + 2.3\sqrt{3} - 4\sqrt{3}$
$= 3\sqrt{3}$
b)
$B = \sqrt{18} + 2\sqrt{2} - \sqrt{50} + \sqrt{24} - \sqrt{54}$
$= \sqrt{9.2} + 2\sqrt{2} - \sqrt{25.2} + \sqrt{4.6} - \sqrt{9.6}$
$= 3\sqrt{2} + 2\sqrt{2} - 5\sqrt{2} + 2\sqrt{6} - 3\sqrt{6}$
$= -\sqrt{6}$
