Slope intercept form is y=mx+b. but how do you get the slope, and the intercept? The formula for slope is
y2-y1
m=----------
x2-x1
so you have 7-9 over 2+2 (minus a negative is plus a positive)
so you have -2/4=-1/2
your slope is -1/2.
so far your equation looks like this: y=-1/2x+b
so now we find B
pick a point and go along the graph. i'll go with (2,7)
use your slope. so at 2,7 go down one and right two. now you're at (0,6)
(0,6) is your Y-Intercept.
now you have your slope (-1/2) and your Y-intercept (6)
slap those together into Slope-intercept form and you get
y=-1/2+6