Answer: 15
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We're asked to find the slope:
m = slope
m = (y2-y1)/(x2-x1)
m = (50-20)/(4-2)
m = 30/2
m = 15
The rate of change is 15. Each time x goes up by 1, y increases by 15.
slope = rise/run = 15/1
rise = 15, run = 1
I used the middle two columns of the table, but you could use any two columns you want. I subtracted the y values together to get the change in y, which is the rise. The change in x, aka run, is the difference in x values. You must subtract the values in the same order. If done in the wrong order, you might get -15 as the incorrect answer.