Question

What is the value of x? x= units

Answer 1

The interior triangles are similar, so the following ratio should hold true:

 9       x
--- = ------           then x^2=144 and x=12 (answer)
 x      16

Answer 2

Triangles RTS and  QTr are similar So 
x/ 16 = 9/x
x^2 = 144

x = 12 (answer)