I'm getting it from the net? Gotcha. Ok, here we go then, I'll do your work.
Given: (4,0) (0,5)
Slope: M =
Y2-Y1
------ = -1.25
X2-X1
Y-intercept: b = y-mx
b = 0 - (-1.25*4) = 5
Point Slope form: y - 5 = -1.25(x-0)
Slope-Intercept Form = Y = mx + b = -1.25x + 5