tolong jwb ya buat besok

Diket: K = 240 cm
panjang : lebar = 7:5
Ditanya: L...?
Jawab: 
K = 2p + 2l
240 = 2p + 2l
120 = p + l
jumlah perbandingan : 7+5 = 12
panjang = 7/12 x 120 = 70 cm
lebar = 5/12 x 120 = 50 cm (a)

K = 240cm
p : l = 7 : 5

K = 2p + 2l
240cm = 2 X 7y + 2 X 5y
240cm = 24y
y = 240cm / 24
y = 10cm

lebar = 5y = 5 X 10 = 50cm
panjang = 7y = 7 X 10 = 70cm