first you have to find the slope given the two points.
m = y2 - y1/ x2 - x1 (3, -1), (4, -3)
m = -3 - (-1)/ 4 - 3
m = -2/1
m = -2
point-slope formula;
y - y1 = m(x - x1)
y - (-1) = -2(x - 3)
y + 1 = -2x + 6
y = -2x + 6 - 1
y = -2x + 5 << your answer
hope this helps, God bless!