When writing linear equations you always use the format y =mx + b, where x and y represent any coordinate (x,y) on the line, m is the slope, and b is the y intercept.
Since you are given the slope you plug it in along with x and y from the coordinate you are given:
0 = -12(4) + b
(y = m(x) + b)
Then you solve for b: 0 = -48 + b
48 = b
When you write your final equation, you only plug in the slope and y intercept to get an equation of:
y = -12x + 48