[tex]a = \sqrt{18}+\sqrt{8} = \sqrt{9\cdot2}+\sqrt{4\cdot2} = \sqrt{9}\cdot\sqrt{2}+\sqrt{4}\cdot\sqrt{2} = 3\sqrt{2}+2\sqrt{2}=\underline{5\sqrt{2}}\\\\b = \sqrt{98}-\sqrt{32} = \sqrt{49\cdot2}-\sqrt{16\cdot2} = \sqrt{49}\cdot\sqrt{2}-\sqrt{16}\cdot\sqrt{2} = 7\sqrt{2}-4\sqrt{2} = \underline{3\sqrt{2}}[/tex]
[tex]Ob = 2(a+b) = 2(5\sqrt{2}+3\sqrt{2}) = 2\cdot8\sqrt{2}\\\\\boxed{Ob = 16\sqrt{2}}[/tex]
