3×1.4+2×(3×0.7+1.4×0.7)
=4.2+2×3.08
=4.2+6.16
=10.36平方分米
做一个长3分米,宽1.4分米,高0.7分米的长方体无盖铁盒,至少要用(10.36 )平方分米的铁皮