Line L has the equation 4y-6x=33. Line M goes through the point A (5,6) and the point B (-4,k). Line L is perpendicular to M. Work out the value of k.

Line L has the equation 4y-6x=33. Line M goes through the point A (5,6) and the point B (-4,k). Line L is perpendicular to M. Work out the value of k.