Please can someone help with this. Answer should be y + 4x = 13 but not sure how to get to this? Where am I going wrong? Find the equation of the line joining points (1,9) and (3,1)

m=y2-y1/x2-1= 1-9/3-1=-8/2=-4

m= -4, a = 3, b= 1

y-b= m(x-a)
y-1=-4(x-3)
y-1=-4x+12
y= -4x + 11?