To find the rate of change, or slope, pick two points. The slope, is change in y coordinates over change in x coordinates.

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In this case, the slope is

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Remember that subtracting a negative number equals adding the number without the negative sign.
a-(-b) = a+b
Now for the y-intercept. The y-intercept is where the graph intersects the y-axis, where x = 0.
You have the coordinate (0, -1), where x = 0. So the y-intercept is -1.
Putting these values into the slope-intercept form y = mx+b, the equation is
y = -5x - 1