6×3-13=
2×4+15=
80-7×9=
30-3×8=
36-9×2=
31-6×2=
4×9-25=
33+3×7=
15+8×4=
6×8-39=
4×3+56=
4×7-12=
5×2+42=
9×1+7=
6×6-18=
10×3+9=
72-8×7=
48-6×7=
20 -3×4=
7×2+16=
5×9-21=
9-4×2=
65+85-30=
11×5-40=
6×9+7=
9×2+34=
68-24-40=
2×5+12=
37-5×5=
7×5-22=
足球上黑色皮共有12块,白色皮比黑色皮的2倍少4块,白色皮共有多少块?