Jawabanmu

2014-04-27T22:17:38+07:00
K = 2 (p+l)
40= 2 (3x +4 + x + 6 )
40 = 2 ( 4x + 10 )
40 = 8x + 20
40 - 20 = 8x
20 = 8x 
x = 20/8
x = 2,5

jadi, panjang = 3x+4 = 3(2,5) +4 = 11, 5cm
       lebar = x + 6 = 2,5 + 6 = 8,5 cm

semoga membantu :)
2014-04-27T22:17:57+07:00
3X + 4 + 3X + 4 + X + 6 + X + 6 = 40, 8X + 20 = 40, 8X = 40 - 20, 8X = 20, 8X : 8 = 20 : 8, X = 2,5, - jadi panjang = 3X + 4 = 3 x 2,5 + 4 = 11,5, lebar = X + 6 = 2,5 + 6 = 8,5 - maaf kalo salah