Since in y=8, the slope is 0 (because there is no x) and b is 8 in y=mx+b, we know that the perpendicular line is x=(something) because the perpendicular lines of y=<number> are x=<number> due to that y=<number> equations are strictly horizontal while x=<number> equations are strictly vertical. Since we know that x=<number> has to pass through (7, 8), x =7