Explanation:
Ok. First, you need to choose two points on the line. Lucky for you, they give you some. Just choose any two, it doesn't really matter. Next, organize the values. This is how I like to do mine: (shown in in attached image)
With this, you'll get an X1, Y1, X2, and Y2 (self-explanatory, look at the numbers on the little table. You'll need to put these in the formula
(Y2-Y1)
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(X2-X1)
this will give you a value with Y being divided (or over) X. Depending on what your teacher wants, divide Y by X and put that in for your answer. Most of the time, you can get away with just putting that little fraction in for your answer.
TROUBLESHOOTING:
a good way to check to make sure you didn't mess up the positive or negative value is to look at the line that those points make. Does it go from the bottom up as you go from left to right? If so, you got a positive value, so your fraction WONT have a negative in front of it. Vice versa for negatives. Does it go down from left to right? Yeah? then you have a negative. In this one, your value should be a positive. Don't slip up on that!! It's common mistake, and an easy one to make .But it's easy to fix!!