4: 图一
(8+8+3+3)×2
=22×2
=44厘米
图二
(3x4+8)x2
=20x2
=40厘米
5: 3+2×2
=7米
6:
(50+40)×2
=90×2
=180厘米
够
7: 100×2+50×2
=200+100
=300米