①4×(250-400÷16)
②5.5÷×
③3.6×+6.4×
④7-7×+
⑤+4.9++5.1
⑥(-0.8+)×12.5
①
②()÷
③
④-(÷-)
⑤19×(+)×37
⑥÷[(-)×6]