Question

Perpendicular to y=1/2x-1, x intercept at 4

Answer 1

y=-2x+8 is the correct y-int equation

Answer 2

The slope of y = (1/2)x - 1 : m = 1/2
Perpendicular line has the slope m' = -1/m = -2.

x intercept at 4 means new line passes through (4,0)
y - 0 = -2(x - 4)
y = -2x + 8