84又4/19×1.375＋105又5/19×0.9
=(21又1/19)*4*1.375＋(21又1/19)*5*0.9
=21又1/19*5.5+21又1/19*4.5
=21又1/19*(5.5+4.5)
=21又1/19*10
=21*10+1/19*10
=210+10/19
=210又10/19