Tìm x biết

$$\begin{gathered} \mathrm{Tìm} \mathrm{x}, \mathrm{biết}: \\ \mathrm{a}, (\mathrm{x}+3)({\mathrm{x}}^2-3\mathrm{x}+9)-\mathrm{x}{(\mathrm{x}-2)}^2=27 \\ \mathrm{b}, (\mathrm{x}-1)(\mathrm{x}-5)+3=0 \end{gathered}$$