tolong pakai cara no 15 dan 16

Nomor 15 :
Perbandingan
3 : 4 = X : 9
4X = 27
X = 27/4
X = 6,75 cm

Nomor 16 :
a : b = 3 : 4
4a = 3b
a = 3b/4
Maka :
(6a+b) : (4a+5b) = (6(3b/4) + b) : (4(3b/4) + 5b)
(6a+b) : (4a+5b) = ((9b+2b)/2) : 8b
(6a+b) : (4a+5b) = 11b : 16b = 11 : 16

Semoga dapat membantu.