1. **State the problem:** Find the difference and write the answer in standard form for the expression $$(9a^2 + 2a) - (4a^2 + 3 - a)$$. 2. **Apply the subtraction:** Distribute the minus sign to each term inside the second parentheses: $$9a^2 + 2a - 4a^2 - 3 + a$$ 3. **Combine like terms:** Group the terms with $a^2$, $a$, and constants: $$ (9a^2 - 4a^2) + (2a + a) - 3 $$ 4. **Simplify each group:** $$ 5a^2 + 3a - 3 $$ 5. **Final answer in standard form:** $$\boxed{5a^2 + 3a - 3}$$