Perpendicular equations have opposite reciprocal slopes, so any equation perpendicular to the equation y = 1/2 x - 2 would have the slope -2.
Now plug in the point (6, -3) into the equation y = -2x + b to find out what b is.
-3 = -2(6) + b
Multiply -2 by 6.
-3 = -12 + b
Add 12.
9 = b
So the equation is y = -2x + 9
Hope this helps