Question 797517
You are right in saying that the opposite reciprocal is the slope of the perpendicular line. Thus the slope of the new line would be {{{-2/1}}} or just {{{-2}}}.

To find the line that crosses x-axis @ 4, you can plug in (4,0) with the new slope.

Using point-slope form:
{{{(y-0)=-2(x-4)}}}
{{{y=-2x+8}}} - Remember to distribute!

This line is perpendicular to {{{y=(1/2)x-1}}} and crosses the x-axis at x=4