\[\boxed{\text{492\ (492).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\text{P\ }(a;64)\]
\[\textbf{а)}\ y = x^{2}\ \]
\[64 = a^{2}\]
\[\ a = \pm 8.\]
\[\textbf{б)}\ y = x^{3}\ \]
\[64 = a^{3}\]
\[a = 4.\ \]