Jawabanmu

2014-05-20T20:36:15+07:00
Lp = 2(pl + pt + lt)
Lp = 2(40x25 + 40x12 + 25x12)
Lp = 2(1000 + 480 + 300)
Lp = 2 x 1780
Lp = 3560 cm²


Maaf kalau ada kesalahan. 
2014-05-20T20:38:26+07:00
Luas selimut balok :
= 2 {(p x l) + (p x t) + (l x t)}
= 2 {(40 x 25) + (40 x 12) + (25 x 12)}
= 2 (1000 + 480 + 300)
= 3560cm²