[20-2{5+ (-12)} x 2(5-2-9)}]

= [20 - 2{5 - 12} $\times $ 2(5 - 11)}], solving simple brackets first

= [20 - 2{-7} $\times $ 2(-6)}]

= [20 - {-14} $\times $ -12], solving curly brackets

= [20 + 14 $\times $ (-12)]

Now we apply multiply operation before addition as per BODMAS rule,

= [20 - 168], solving square brackets

= -148 (answer)

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