The expression $3x + y$ is a linear expression with two variables, $x$ and $y$. It represents a line in two-dimensional space when graphed.

If you'd like to solve, simplify, or analyze this further, I’ll need more context, such as:

• A specific value for $x$ or $y$.
• An equation to set $3x + y$ equal to (e.g., $3x + y = 10$).
• Constraints or additional expressions involving $x$ and $y$.

Would you like to proceed with a specific operation or context? Let me know!

Questions to Explore Further:

1. Do you want to solve $3x + y$ for a given value of $x$ or $y$?
2. Should this expression be graphed as a line on a coordinate plane?
3. Would you like to solve for one variable in terms of the other (e.g., $y$ in terms of $x$)?
4. Is there a specific application of this expression, such as in a word problem or equation system?
5. Are you exploring linear equations, or is this part of a larger problem?

Tip: Always define what you need from an expression to make it more specific and actionable!