Answer:
1/2
Explanation:
The slope of a line perpendicular to any given line is the negative reciprocal of the given line's slope:

In this problem, the slope of the given line is
(rise over run).
So, to find the slope of a line that is perpendicular to it, we simply flip the given line's slope and change its sign.

So, a line which is perpendicular to the given line would have a slope of 1/2.