Well your line travels parallel to the y axis. What's perpindicular to the y axis? The x axis. So all lines perpindicular to the line traveling vertically through (4, 0) are parallel to the x axis. Now we need to find the intercept of this line, which they give you as (-2, 3).
A horizontal line that passes through -2, 3? We can put this into an equation and see what happens.
y - y1 = m(x - x1)
y - 3 = 0(x - (-2))
y - 3 = 0
y = 3
