8th grade math please help! 8-10 points

The third one, this is because you take your y2 and y1 values (y2=0 and y1=9 because these are the two y values given to you from each coordinate) and subtract 0-9. then you do the same, but with the x2 and x1 values. so your x1 value is 3 and your x2 value is 0, so you subtract 0 from 3. divide your second answer from the first answer, to get a gradient of -1/3 x. now using the first coordinate (0,9) you know that the y coordinate is 9. as the x value =0, we know that the line is passing through the y axis at 9 so 9 is your y intercept. this gives you the equation -1/3x+9. hope this helped and wasn't too confusing!

So the first question
cost =y
estimated cost=cost of toy+cost of batteries
so
y=12+0.75x or y=0.75x+12 or the third choice