1. **State the problem:** Simplify the expression $6a - [3 - (5 - 3a)] - 4$. 2. **Recall the rules:** When simplifying expressions with brackets, start from the innermost brackets and work outward. Remember to distribute negative signs when removing brackets. 3. **Simplify inside the innermost brackets:** $$3 - (5 - 3a) = 3 - 5 + 3a = -2 + 3a$$ 4. **Substitute back into the expression:** $$6a - [-2 + 3a] - 4$$ 5. **Remove the brackets by distributing the negative sign:** $$6a + 2 - 3a - 4$$ 6. **Combine like terms:** $$6a - 3a + 2 - 4 = 3a - 2$$ **Final answer:** $$3a - 2$$