Answer:
[tex]y= -3x+9[/tex]
Step-by-step explanation:
We can easily see from the graph that the equation intersecs the x-axis at p=3 and the y-axis at q=9. Now there is a trick to quickly write the equation in these situations, and it is
[tex]\frac xp + \frac yq = 1[/tex] where p and q are the length of the segments (with their sign!!) the line cuts from the origin.
At this point, it's just a matter of writing the equation in the wanted form:
[tex]\frac x3 + \frac y9 =1\\9\frac x3 + y = 9\\y= -3x+9[/tex]
Which is the equation you want.
If you prefer a more traditional approach, you can determine the slope right away by noticing that when the y coordinate moves from 9 to 0, ie it decreases by 9, the x coordinate goes from 0 to 3, and the slope is [tex]m= {\Delta y \over \Delta x} = {{-9}\over{3}} = -3[/tex]
