Answer:
x < 13
General Formulas and Concepts:
Pre-Algebra
Order of Operations: BPEMDAS 
- Brackets 
- Parenthesis 
- Exponents 
- Multiplication 
- Division 
- Addition 
- Subtraction 
Equality Properties
Explanation:
Step 1: Define
3x < 39
Step 2: Solve for x
- Divide 3 on both sides: x < 13
Here we see that any value x smaller than 13 would work as solution to the inequality.