If x225+y264=1\displaystyle {\frac{{{x}^{{2}}}}{{{25}}}}+{\frac{{{y}^{{2}}}}{{{64}}}}={1} and y(3)=6.4\displaystyle {y}{\left({3}\right)}={6.4}, find y(3)\displaystyle {y}'{\left({3}\right)} by implicit differentiation.

y(3)\displaystyle {y}'{\left({3}\right)} =