16.8*[（2.4+三分之一）/1.12-一又六分之五]
=16.8*(2.4+1/3)/1.12-16.8*7/6
=15*(2.4+1/3)-2.8*7
=15*2.4+15*1/3-19.6
=36+5-19.6
=11.4