keliling suatu persegi panjang 42 cm,jika selisih panjang dan lebar 3 cm,maka luas persegi panjang adalah?

misal
p = x
l = x - 3

K = 2 × ( p + l )
42 = 2 × ( x + x - 3 )
42 ÷ 2 = 2x - 3
21 = 2x - 3
2x = 21 + 3
2x = 24
x = 12

jadi
p = x = 12
l = x - 3 = 12 - 3 = 9
L = p × l
= 12 × 9
= 108 cm²