slope = 7/3
perpendicular slope = -3/7
remember how slope = rise over run? in equation form that's:
m = (y2 - y1) / (x2 - x1)
m is the slope
(x1,y1) is one point
(x2,y2) is the other point
so, plugging in numbers:
m = (y2 - y1) / (x2 - x1)
-3/7 = (y - -2) / (4 - -3)
-3/7 = (y + 2) / 7
-3 = y + 2
y = -5