a: \(542\cdot7+542\cdot2+542\)
\(=542\left(7+2+1\right)\)
\(=542\cdot10=5420\)
b: \(\left(126\cdot35+157\cdot55\right)\cdot\left(132-6\cdot22\right)\)
\(=\left(126\cdot35+157\cdot55\right)\left(132-132\right)\)
\(=0\cdot\left(126\cdot35+157\cdot55\right)\)
=0
c: \(897\cdot99+897\)
\(=897\left(99+1\right)\)
\(=897\cdot100=89700\)