Answer:
30
General Formulas and Concepts:
Pre-Algebra
Order of Operations: BPEMDAS 
- Brackets 
- Parenthesis 
- Exponents 
- Multiplication 
- Division 
- Addition 
- Subtraction 
Explanation:
Step 1: Define
6² + x - x²
x = 3
Step 2: Evaluate
- Substitute in x: 6² + 3 - 3²
- Exponents: 36 + 3 - 9
- Add: 39 - 9
- Subtract: 30