28+120×8 730-230÷10+42 420×15÷21+51 （75+360）÷（20-5)
=7×4+240×4 =730-23+42 =420÷21×15+51 =(75+360)÷15
=（7+240）×4 =730+42-23 =20×15+51 =75÷15+360÷15
=247×4 =772-23 =300+51 =5+24
=988 =749 =351 =29