jwblh no 1 sjaa, trmksh yg bntu(:

keliling = a + b + c = 30 cm
            = 1 + 2 + 3 = 30
            = 6 = 30
            = 30 : 6
            = 5

a = 1 x 5
   = 5 cm

b = 2 x 5
   = 10 cm
 
c = 3 x 5
   = 15 cm

maaf kalo salah ya