Xenia has $1 more than Yanni.

To do this, make a chart as follows:

Now fill in each column of the chart assuming that Xenia has that number of dollars. For example, if Xenia has $1, then Yanni has $0. And if Xenia has $2, then Yanni has $1. Continue until your chart looks like this:

Now you have five pairs of points that you can plot on your graph as (Xenia, Yanni): (1, 0), (2, 1), (3, 2), (4, 3), and (5, 4). Next, draw a straight line through these points, as shown in the below figure.

Here’s a slightly more complicated example:

Yanni has $3 more than twice the amount that Xenia has.

Again, start by making the usual chart:

You can fill in this chart by supposing that Xenia has a certain amount of money and then figuring out how much money Yanni would have in that case. For example, if Xenia has $1, then twice that amount is $2, so Yanni has $3 more than that, or $5. And if Xenia has $2, then twice that amount is $4, so Yanni has $3 more, or $7. Continue in that way to fill in the chart as follows:

Now you can plot these five points on the graph and draw a line through them.