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):
![6+2[-8-6x-12]+10x](https://img.qammunity.org/2019/formulas/mathematics/high-school/wy08htqte9m5icl6p31cti3hlqtyp6xe6z.png)
Next, combine like terms:
![6+2[-6x-20]+10x](https://img.qammunity.org/2019/formulas/mathematics/high-school/nmpe1i5kiyym60t7usv1ub74hm8svdabe3.png)
Next, distribute 2 to [-6x - 20]:
![6-12x-40+10x](https://img.qammunity.org/2019/formulas/mathematics/high-school/dnkuy82d492sxtq3br3n6pwilg17i9vrjf.png)
Lastly, combine like terms and your final answer will be
![-2x-34](https://img.qammunity.org/2019/formulas/mathematics/high-school/bmrpo7t8xkxnpeaqk6r6w9k3qau86hwdkw.png)