Find the compounded ratio of:

(i) 2 : 3 and 4 : 9

(ii) 4 : 5, 5 : 7 and 9 : 11

(iii) (a - b) : (a + b), (a + b)² : (a² + b²) and (a⁴ - b⁴) : (a² - b²)²