（1）6.73×4.8+5.2×6.73
=（4.8+5.2）×6.73
=10×6.73
=67.3；
（2）1.6×[（12-7.2）÷（0.84÷2.1）]
=1.6×[4.8÷0.4]
=1.6×12
=19.2；
（3）81÷[（3.25+6.75）×0.09]
=81÷[10×0.09]
=81÷0.9
=90；
（4）0.45×78.2+20.8×0.45+0.45
=0.45×78.2+20.8×0.45+0.45×1
=0.45×（78.2+20.8+1）
=0.45×100
=45．