[tex]15:[11-(7*5-9*9:x:3):8+2*4]*3=3\\
15:[11-(7*5-9*9:x:3):8+2*4] = 1\\
15 = 11-(7*5-9*9:x:3):8+2*4\\
15 = 11-(7*5-9*9:x:3):8+8\\
7 = 11-(7*5-9*9:x:3):8\\
4 = (7*5-9*9:x:3):8\\
32 = 7*5-9*9:x:3\\
32 = 35 - 81:x:3\\
32 = 35 - 27:x\\
27:x = 3 =\ \textgreater \ x = 9
[/tex]