45÷5/7÷21=45*7/5*1/21＝3 (5/8-1/6）×24=5/8*24-1/6*24＝15-4＝113/20×【（3/5-1/3)÷0.6】＝3/20*（4/15*5/3）＝3/20*4/9＝1/15
