(-15又2/3)-[-13又2/3+(-31又2/15)+14]
=-15又2/3-(-13又2/3-31又2/15+14)
=-15又2/3+13又2/3+31又2/15-14
=-2-14+31又2/15
=-16+31又2/15
=15又2/15
去括号
负正得负
正负得负
负负得正