1. **State the problem:** Simplify the expression $$3(4x^2 + x) - (3x^2 + 3x - 1)$$. 2. **Apply the distributive property:** Multiply each term inside the parentheses by the factor outside. $$3 \times 4x^2 = 12x^2$$ $$3 \times x = 3x$$ So, $$3(4x^2 + x) = 12x^2 + 3x$$ 3. **Distribute the negative sign to the second parentheses:** $$-(3x^2 + 3x - 1) = -3x^2 - 3x + 1$$ 4. **Combine the expressions:** $$12x^2 + 3x - 3x^2 - 3x + 1$$ 5. **Group like terms:** $$ (12x^2 - 3x^2) + (3x - 3x) + 1$$ 6. **Simplify each group:** $$12x^2 - 3x^2 = 9x^2$$ $$3x - 3x = 0$$ So the expression becomes: $$9x^2 + 0 + 1 = 9x^2 + 1$$ 7. **Final answer:** The simplified expression is $$9x^2 + 1$$. This means the sign and number attached to $x^2$ is $9$ and the constant term is $+1$.