Slope intercept is y=mx+b with m as slope and b as y intercept. Since the line goes through the vertical line, the y-axis, at 0,7, the y intercept is 7.
y=mx+7
Slope is rise/run, so since you're going down 5 and to the right 8, your slope is -5/8. So, y=-(5/8)x+7 is your answer.