Don't get confused with the second pair of brackets - you must apply the negative sign on the outside to all the signs on the inside, which now gives:
[tex](4 x^{3}-12 x^{2} -5)+8 x^{2} -4x-3 [/tex]
Now just take away the brackets and collect like terms to get:
[tex]4 x^{3} -12 x^{2} -5+8 x^{2} -4x-3= 4 x^{3} -4 x^{2} -4x-8[/tex]
