First of all we are going to find the slope perpendicular to the equation y = -1/2 x +6.
We need to remember that two slopes are perpendicular if its product is equal to -1. Like this:

Now, we find the equation of the line using the general form:

m - slope

That was a point of the line, now:

Finally, the equation of the line that passes through (-4,2) and is perpendicular to the equation y = -1/2x+6 is
y=2x+10