first find the slope;
m = y2 - y1/ x2 - x1 (2, 1) (3, 3)
m = 3 - 1/ 3 - 2
m = 2/1
m = 2
now find the equation with the point-slope formula;
y - y1 = m(x - x1) m = 2 (2, 1)
y - 1 = 2(x - 2)
y - 1 = 2x - 4
y = 2x - 4 + 1
y = 2x - 3 <<< the equation.
hope this helps, God bless!