Question

(x-9):(3x+6) is the triplicate ratio of 4:9 find x.

Answer 1

x-9 : 3x + 6 is the triplicate ratio of 4 : 9. 
hence, 4^3:9^3 = x-9:3x+6

that is, 

64/729 = x-9 / 3x + 6

ie, 

192x + 384 = 729x - 6561 
537x = 6945
therefore x = 6945/537
 hence x = 2315/179