[3/4-7/8/(5/6+4/5)]*28=[3/4-7/8÷49/30]*28=[3/4-15/28]*28=3/4*28-15/28*28=21-15=6(1.25*4/5-0.76)/(1又3/8+1又1/40）=(1-0.76)/2.4=0.24/2.4=0.1[(0.2+1/3)*4.5]/(8又1/20-6.45）=8/15*4.5/1.6=2.4/1.6=1.5x+3...