Answer:
6x + 3
General Formulas and Concepts:
Pre-Algebra
Distributive Property
Order of Operations: BPEMDAS 
- Brackets 
 - Parenthesis 
 - Exponents 
 - Multiplication 
 - Division 
 - Addition 
 - Subtraction 
 
Explanation:
Step 1: Define
3(2x + 1)
Step 2: Expand
- Distribute 3: 3(2x) + 3(1)
 - Multiply: 6x + 3