`64 xx 4^n = 4^5`

`=> 4^3 xx 4^n = 4^5`

`=>             4^n = 4^5 : 4^3`

`=>             4^n = 4^2`

`=>                n  = 2`

`x` x `6,3 = 187`

`=> x    = 187 : 6,3`

`=> x     = 1870/63`

\(\dfrac{11}{9}-\dfrac{4}{3}+\dfrac{7}{9}\)

\(=\dfrac{11}{9}-\dfrac{12}{9}+\dfrac{7}{9}\)

\(=\dfrac{11-12+7}{9}\)

\(=\dfrac{6}{9}=\dfrac{2}{3}\)

`(2x+1)^2 = 100`

`=> (2x + 1)^2 = 10^2`

`=>` \(\left[{}\begin{matrix}2x+1=10\\2x+1=-10\end{matrix}\right.\)

`<=>`\(\left[{}\begin{matrix}2x=9\\2x=-11\end{matrix}\right.\)

`<=>` \(\left[{}\begin{matrix}x=\dfrac{9}{2}\\x=-\dfrac{11}{2}\end{matrix}\right.\)

\(5^{11}.5^4=5^{11+4}=5^{15}\)

\(11^7.11^5=11^{7+5}=11^{12}\)

`\(3.9.27.81=3^1.3^2.3^3.3^4=3^{1+2+3+4}=3^{10}\)

\(5^{16}:5^{12}.5^2=5^{16-12+2}=5^6\)