Помогите решить !!пожалуйста

4. a)
$\left \{ {{2^{y-1}=4^{0,5x}}, \atop { log_{3}(7x+y) =2};}} \right. \\ \left \{ {{2^{y-1}=2^x,} \atop {7x+y=9;}} \right. \\ \left \{ {{y-1=x,} \atop {7x+y=9;}} \right. \\ \left \{ {{y-1=x,} \atop {7(y-1)+y=9;}} \right. \\ 7y-7+y=9; \\ 8y=16; \\ y=2. \\ x=2-1=1. \\ \left \{ {{x=1,} \atop {y=2.}} \right. \\$
Ответ: (1;2).

б)
$\left \{ {{ \frac{1}{ \sqrt{x}}+ \frac{1}{ \sqrt{y}}= 1,} \atop { \sqrt{x} + \sqrt{y}=4; }} \right. \\ \left \{ {{\frac{ \sqrt{x}+ \sqrt{y} }{ \sqrt{x} * \sqrt{y}}=1,} \atop {\sqrt{x}=4- \sqrt{y}; }} \right. \\ \left \{ {{ \frac{4}{\sqrt{x}* \sqrt{y}}=1 } \atop { \sqrt{x}=4- \sqrt{y} ; }} \right. \\ \left \{ {{\sqrt{x}* \sqrt{y}=4} \atop {\sqrt{x}=4- \sqrt{y};}} \right. \\ (4- \sqrt{y})* \sqrt{y}=4; \\ y-4 \sqrt{y}+4=0; \\ t= \sqrt{y} ; \\ t^2-4t+4=0; \\ (t-2)^2=0; \\ t=2; \\$
$\sqrt{y}=2; \\ y=4; \\ \sqrt{x} =4- \sqrt{4}=4-2=2; \\ x=4; \\ \left \{ {{x=4,} \atop {y=4.}} \right. \\$
Ответ: (4;4).

5.
$(-27^{ \frac{1}{3} })^{2}* \sqrt[5]{-9^{10}}*( \frac{-3}{\sqrt[6]{81}} )^{-6}=-(3^{3* \frac{1}{3} })^2*(3^{2})^{ \frac{10}{5}}*( \frac{3}{3^{ \frac{4}{6}}})^{-6}= \\ =-3^2*3^4*(3^{1- \frac{2}{3}})^{-6}=-3^2*3^4*(3^{ \frac{1}{3}})^{-6}= \\ =-3^2*3^4*3^{-2}=-3^4=-81.$