\(B=\left(\dfrac{3x-5\sqrt{x}-2}{9x-1}-\dfrac{1}{1-3\sqrt{x}}\right)\cdot\left(\dfrac{4}{1-\sqrt{x}}-1\right)\\ =\left[\dfrac{\left(\sqrt{x}-2\right)\left(3\sqrt{x}+1\right)}{\left(3\sqrt{x}+1\right)\left(3\sqrt{x}-1\right)}+\dfrac{1}{3\sqrt{x}-1}\right]\cdot\left(\dfrac{4}{1-\sqrt{x}}-1\right)\\ =\left(\dfrac{\sqrt{x}-2}{3\sqrt{x}-1}+\dfrac{1}{3\sqrt{x}-1}\right)\cdot\dfrac{4-\left(1-\sqrt{x}\right)}{1-\sqrt{x}}\\ =\dfrac{\sqrt{x}-2+1}{3\sqrt{x}-1}\cdot\dfrac{\sqrt{x}+3}{1-\sqrt{x}}\\ =\dfrac{\sqrt{x}-1}{3\sqrt{x}-1}\cdot\dfrac{\sqrt{x}+3}{-\left(\sqrt{x}-1\right)}\\ =\dfrac{\sqrt{x}+3}{-\left(3\sqrt{x}-1\right)}=\dfrac{\sqrt{x}+3}{1-3\sqrt{x}}\)
\(B=\left(\dfrac{3x-5\sqrt{x}-2}{9x-1}-\dfrac{1}{1-3\sqrt{x}}\right)\cdot\left(\dfrac{4}{1-\sqrt{x}}-1\right)\)
\(=\dfrac{3x-5\sqrt{x}-2+3\sqrt{x}+1}{\left(3\sqrt{x}-1\right)\left(3\sqrt{x}+1\right)}\cdot\dfrac{4-1+\sqrt{x}}{1-\sqrt{x}}\)
\(=\dfrac{3x-2\sqrt{x}-1}{\left(3\sqrt{x}-1\right)\left(3\sqrt{x}+1\right)}\cdot\dfrac{3+\sqrt{x}}{1-\sqrt{x}}\)
\(=\dfrac{\left(\sqrt{x}-1\right)\left(3\sqrt{x}+1\right)}{\left(3\sqrt{x}-1\right)\left(3\sqrt{x}+1\right)}\cdot\dfrac{\sqrt{x}+3}{-\left(\sqrt{x}-1\right)}=\dfrac{-\left(\sqrt{x}+3\right)}{3\sqrt{x}-1}=\dfrac{\sqrt{x}+3}{1-3\sqrt{x}}\)
