The slope of a line that is perpendicular to another line is the negative reciprocal of the other.
In this case, we know that the slope of the given equation is 2.
Since we're solving for a line perpendicular to it, we simply find the reciprocal of the 2 (It turns into 1/2) and make it negative.
y = -1/2x + b
Since the given states that the new y-intercept is 10, input it into 'b'.
y = -1/2x + 10
If you'd like me to explain anything I did here, just ask :)
-T.B.
