In order to determine the equation of the line, use the following general form:
y - y = m(x - xo)
where m is the slope and (xo,yo) is a point of the line.
In this case m = 3 and (xo,yo) = (12,33).
Replace the previous values into the general expression, and solve for y:
y - 33 = 3(x - 12)
y - 33 = 3x - 36
y = 3x - 36 + 33
y = 3x - 3
Hence, the equation of the line is
y = 3x - 3
