You have provided the following set of expressions:

1. $a + b + c$
2. $-3a + b + c$
3. $a - 3b + c$
4. $a + b - 3c$

Would you like to simplify these, perform some specific operations on them (like addition, subtraction, etc.), or analyze them in some way?

Let me know if you have any specific instructions or questions!

Here are five related questions for exploration:

1. How would the expressions change if each variable ($a$, $b$, $c$) is substituted with specific values?
2. What would happen if all the terms in each expression were multiplied by a constant factor (e.g., 2)?
3. Can you factor any of these expressions in terms of a common variable?
4. How would you solve these if they were part of a system of equations?
5. What is the result of adding or subtracting two or more of these expressions?

Tip: When dealing with expressions like these, look for patterns or common factors to simplify them or combine them efficiently.