We have, <A = <CED

In ΔCAB and ΔCED

<C = <C (Common)

<A = <CED (Given)

Then, ΔCAB ~ ΔCED (By AA similarity)

So, (Corresponding parts of similar triangle area proportion)

Or,15/9 = 9/x

Or, 15x = 90

Or, x = 90/6

Or, x = 6cm.