Here’s an example:

Jacob is exactly 5 years younger than Marnie, and together their ages add up to 15. How old are they?

To solve this problem, first make a chart to show that Jacob is 5 years younger than Marnie:

Then make another chart to show that together, the two children’s ages add up to 15:

Finally, plot both lines on a graph where the horizontal axis represents Jacob’s age and the vertical axis represents Marnie’s age:

Notice that the two lines cross at the point where Jacob is 5 and Marnie is 10 years old, so these are the two children’s ages.