17.85-（4-0.26）-5.56
=17.85-4+0.26-5.56
=13.85-5.3
=8.5517.85+3.74-5.56=17.85+（3.75-0.01）-（5.55+0.01）=17.85+3.75-5.55-0.02=21.6-5.55-0.02=16.05-0.02=16.03