The
<u>correct answer</u> is:
Matthew's rate is higher by $50 per month.
Explanation:
We know that Christopher's rate is $550 per month.
To find Matthew's rate, we will treat the data we have as ordered pairs:
(3, 1800)
(6, 3600)
(9, 5400)
We find the slope of the line between these points. The formula for slope is:

Using the first two points, we have:

To verify Matthew saves the same amount each month, we will find the slope between the second two points and make sure they're the same:

Matthew's rate is $600 per month.
This is higher than Christopher's by 600-550=$50 per month.