\(2\times\left(x-51\right)=2\times2^3+20\)
\(2\times\left(x-51\right)=2^4+20\)
\(2\times\left(x-51\right)=16+20\)
\(2\times\left(x-51\right)=36\)
\(x-51=36:2\)
\(x-51=18\)
\(x=18+51\)
\(x=69.\)
\(70-5\times\left(x-3\right)=45\)
\(5\times\left(x-3\right)=70-45\)
\(5\times\left(x-3\right)=25\)
\(x-3=25:5\)
\(x-3=5\)
\(x=5+3\)
\(x=8.\)