（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．