perpendicular means a line that is opposite and reciprocal to the slope you have now
1) first solve for y
5y= -(2x) + 20
y= -(2/5)x + 4
so the slope is -2/5 so perpendicular is m= 5/2
so now use point slope
y-y1=m(x-x1)
m=5/2 and point is (10,-4)
plug and chug
y+4 = (5/2) (x-10 )
y= 5/2x - 25 - 4
y=5/2x - 29
hope i didnt make an adding error
but thats how you do it.
hope that helps