According to the slope formula, if you have a line with slope a and which passes through the point (b, c), the equation of the line will be (y - c) / (x - b) = a.
Since the slope is 4 and the point which the line passes through is (-1, 12), the equation of the line is:
(y - 12) / (x - (-1)) = 4
(y - 12) / (x + 1) = 4
y - 12 = 4(x + 1)
y - 12 = 4x + 4
y = 4x + 4 + 12
y = 4x + 16, which is the equation you need.