0.7*1又九分之四+2又四分之三+(-15)+0.7*九分之五+四分之一*(-15)
=0.7*13/9+11/4+(-15)+0.7*5/9-15/4
=0.7*(13/9+5/9)+11/4-15/4
=0.7*2-1
=0.4