b)
x=2-5\sqrt7
y=1-\sqrt7
\frac{x}{y}=\frac{2-5\sqrt7}{1-\sqrt7}=\frac{(2-5\sqrt7)(1+\sqrt7)}{(1-\sqrt7)(1+\sqrt7)}=\frac{2+2\sqrt7-5\sqrt7-5*7}{1^2-(\sqrt7)^2}=
\frac{-33-3\sqrt7}{-6}=\frac{-3(11+\sqrt7)}{-6}=\frac{11+\sqrt7}{2}
c)
\frac{x}{y}=\frac{4+5\sqrt2}{3+3\sqrt2}=\frac{(4+5\sqrt2)(3-3\sqrt2)}{(3+3\sqrt2)(3-3\sqrt2)}=\frac{12-12\sqrt2+15\sqrt2-15*2}{3^2-(3\sqrt2)^2}=
\frac{-18+3\sqrt2}{9-9*2}=\frac{-3(6-\sqrt2)}{-9}=\frac{6-\sqrt2}{3}=\frac{6}{3}-\frac{\sqrt2}{3}=2-\frac{1}{3}\sqrt2