15-3= 9+8= 18-5= 4+7= 6-4=
6+9= 17-5= 5+8= 10-4= 7+6=
8-3= 4+8= 17-3= 5+7= 16-2=
16-2-4= 2+10+4= 8-2+4= 3+2+6= 9+9-2=