y=mx+b is the formula. So -8=-3x+5would be the answer..
since (x,y) just substitute these numbers you have it into the formulas... Take y from (5,-8) and place it into y=mx+b. Next take the slope which is -3. And then since its a postive number we <em>add</em> are x from (x,y). -8=-3x+5. We also add x next to the slope (-3) becuase we are trying to solve for x. And we <em>always</em> put it next to the slope. Hope this helps!
I'm pretty sure the answer is D. because I don't think anyone would want to take their total meal cost and then multiply it by their tip to make it even larger. You would just add the tip to the meal cost.