18分之7*5+18分之1*15
=(5/18)(7+3)
=(5/18)*10
=50/18
=25/9
=2又7/9
4.2/0.125=4200/125=840/25=168/5=33.6
13.7-26.4÷（2.6+1.4）
=13.7-26.4÷4
=13.7-6.6
=7.1