\(91.\left\{195:\left[84-\left(21+16x\right)\right]\right\}=7\)
\(195:\left[84-\left(21+16x\right)\right]=\frac{7}{91}\)
\(195:\left[84-\left(21+16x\right)\right]=\frac{1}{13}\)
\(84-\left(21+16x\right)=195:\frac{1}{13}\)
\(84-\left(24+16x\right)=195.13\)
\(84-\left(24+16x\right)=2535\)
\(24+16x=84-2535\)
\(24+16x=-2451\)
\(16x=-2451-24\)
\(16x=-2475\)
\(x=\frac{-2475}{16}\)
vay \(x=\frac{-2475}{16}\)