a) \(B=\dfrac{\sqrt{25}+3}{\sqrt{25}+1}=\dfrac{5+3}{5+1}=\dfrac{8}{6}=\dfrac{4}{3}\)
b) \(A=\dfrac{\sqrt{x}\left(\sqrt{x}+2\right)+\sqrt{x}-1-3\sqrt{x}}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+2\right)}=\dfrac{x+2\sqrt{x}+\sqrt{x}-1-3\sqrt{x}}{\left(\sqrt{x}-1\right)\left(\sqrt{x+2}\right)}=\dfrac{x-1}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+2\right)}=\dfrac{\sqrt{x}+1}{\sqrt{x}+2}\)