Okay, let me just make this a little clearer. Hopefully, this is what you meant:
A. y - 8 = -4(x + 4) B. y - 8 = 4(x + 4) C. y + 8 = 4(x - 4) D. y + 8 = -4(x - 4)
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This can also be written as y2 - y1 = m(x2 - x1).
Your M is your slope.
Both A and D have their m as a negative 4. Because you are looking for a positive slope, immediately cancel those answers.
* note that you could have also put them in a more standard form and discovered m which is the x in bx.
Now, you are looking for an equation that contains (4,-8).
Because it is written as y2-y1, your y's are actually points if you were to find another slope or something. This part is a bit hard to explain, but -8 is only found in the y coordinate place in answer B. Your answer would be B. For more explanation on that, there's this great site called coolmath.com and if you search for finding the equation of two points, it explains it much better on there, but I would not want to plagiarize.
2 years is the same as 24 months, so the equation would be: 685 = 24x + 85, where x is the monthly fee. 600 = 24x 600/24 = x x = 25 The monthly fee is $25.
