keliling sebuah persegi panjang 72 cm.jika perbandingan panjang dan lebarnya 7:5,luasnya adalah..... cm

k=2(p+l)
72=2(7x+5x)
36=12x
3=x

p= 7x=7(3)=21
l=5x=5(3)=15

L=pxl
= 21x15=315

2X x (p + l) = 72cm
2X x (7 + 5) = 72cm
2X x 12 = 72cm
24X = 72cm
X = 72cm : 24 = 3cm

p = 7X = 7 x 3cm = 21cm
l = 5X = 5 x 3cm = 15cm

L = p x l = 21cm x 15cm = 315cm2