So with more than one pair of parentheses, you must start from the inside and make your way outside.
So firstly, distribute -3 to (2x + 4):
[tex]6+2[-8-6x-12]+10x[/tex]
Next, combine like terms:
[tex]6+2[-6x-20]+10x[/tex]
Next, distribute 2 to [-6x - 20]:
[tex]6-12x-40+10x[/tex]
Lastly, combine like terms and your final answer will be [tex]-2x-34[/tex]