Jawabanmu

2014-04-20T12:25:20+07:00
K = 2p+2l
57 = 2.9 +2l
57=18+2l
39=2l
l = 19,5

L= p*l
  = 9 * 19,5
=175,5
2014-04-20T12:26:22+07:00
Lebar = (57 - (2 × 9)) : 2
        = (57 - 18) : 2
        = 19,5 cm
luas = 19,5 × 9
       = 175,5 cm²