13-2= 3+7= 6+9= 15+4= 10+5=
8-8= 6+6= 8+3= 6+7= 17-7=
0+4= 16-10= 12-0= 9+9= 7+8=
18-2-3= 9+3+ 4= 4+9-3= 17-2+3=