perbandingan panjang dan lebar persegi panjang 3:1. jika keliling persegi panjang tersebut 72 cm, luasnya adalah...?

2 x (p + l) = 72cm
2 x (3x + 1x) = 72cm
2 x 4x = 72cm
8x = 72cm
x = 72cm : 8 = 9cm

p = 3x = 3 x 9cm = 27cm
l = 1x = 1 x 9cm = 9cm

L = p x l
= 27cm x 9cm
= 243cm²