if the line is perpendicular then the slope is the negative reciprocal
m for the given line is 1 so the perpendicular slope is -1
the equation for a line given the slope and a point is
y-y1 = m(x-x1)
y-(-1) = -1(x-4)
y+1 = -1(x-4)
y+1 = -x+4
y= -x+3
