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What is the rule for this table?
X= 3,6,9
Y= 5, 10, 15
I cant figure it out for my sons 3rd grade math!

data points
data points  

determine rise and run
determine rise and run  
If you graph the data points (3, 5), (6, 10), and (9, 15), you can draw a straight line through them.
The rule for the table is the equation of that line.

Use two of the points to calculate the slope of the line.
rise = 15 - 10 = 5
run = 9 - 6 = 3
slope = rise/run = 5/3

Use the slope and one of the points (say, (6, 10)) to determine the equation of the line.
y - 10 = (5/3)(x - 6)
This equation is in "point-slope" form. However,  "slope-intercept" form is more convenient for filling in a data table.

Convert the equation to slope-intercept form:
y = (5/3)x

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