To find the expression for the perimeter of the triangle, we need to add up the lengths of all its sides.

The given sides of the triangle are labeled as:

• One side is $4x$,
• Another side is $5x$,
• The third side is $3$.

The perimeter $P$ of the triangle is simply the sum of these three sides:

$P = 4x + 5x + 3$

Now, simplifying the expression:

$P = 9x + 3$

So, the expression for the perimeter of the triangle is $9x + 3$.

Would you like more details on this solution, or do you have any questions?

Here are 5 related questions you might want to explore:

1. What happens to the perimeter if $x = 2$?
2. Can you calculate the perimeter for a specific value of $x$?
3. What would the perimeter be if the triangle were equilateral?
4. How does the perimeter change as $x$ increases or decreases?
5. How can the triangle's area be calculated if more information is given?

Tip: In problems like this, always check if the variables can be factored or simplified before finalizing your answer.