We have similar triangles RST ,TSR and TRQ.The triangles are similar to each other .
Similar triangles have sides in proportion.
In similar triangles TQR and TRS:
[tex]\frac{TR}{ST} =\frac{TQ}{TR}[/tex]
Or,
[tex]\frac{x}{9} =\frac{16}{x}[/tex]
Cross multiplying
[tex]x^{2}=16(9)[/tex]
[tex]x^{2}=144[/tex]
Taking root
x=12.
