I cant see any of ur links...
(0,9),(3,0)
slope = (0 - 9) / (3 - 0) = -9/3 = -3
y = mx + b
slope(m) = -3
ur y int (b) is when x = 0....u already have the point (0,9)...so ur y int is 9
so ur equation is : y = -3x + 9....because u have a slope of -3 and a y int of 9