To understand trends in line graphs, here’s what you should do:

1. Look at the Axes: Check out the $x$-axis (this is the horizontal line) and the $y$-axis (this is the vertical line). They show different types of information.

2. Notice Changes: See if the line goes up, down, or stays the same over time. For example, if the line moves from $3$ to $8$ between the first year and the third year, that means it went up by $5$ units.

3. Find the Rate: This is the slope. If the line goes from $10$ to $30$ over $5$ units, you can find the rate by doing the math: $\frac{30 - 10}{5} = 4$ units for each interval.

4. Spot Patterns: Look for regular trends, like cycles or sudden jumps. These changes might show important events happening.