9.47-3.87-2013=9.47-3.47-0.4-2013=6-0.4-2013=6-2013-0.4=-2007-0.4=-(2007+0.4)=-2007.4
9.47-3.87-2.13=9.47-(3.87+2.13)=9.47-6=3.47