Tìm x, y

Tìm x, y, biết :
$$\begin{gathered} a) {(x-\frac{2}{9})}^3={\left(\frac{2}{3}\right)}^6 \\ b) {(8x-1)}^{2x+1 }= 5^{2x+1} \\ c) {(x - 3,5)}^2 + {(y - \frac{1}{10})}^4\le 0 \end{gathered}$$

(GIUP MINH VOI, LAM ON)