ANSWER
y = -3x
Step-by-step explanation
We have to determine the slope-intercept form of the equation of the line.
The slope-intercept form of a linear equation is given as:
y = mx + c
where m = slope
c = y intercept
First, we have to find the slope:

where (x1, y1) and (x2, y2) are two points the line passes through.
Therefore:

Now, we have to use the point-slope method to find the equation:
y - y1 = m(x - x1)
=> y - (-3) = -3(x - 1)
y + 3 = -3x + 3
y = -3x + 3 - 3
y = -3x
That is the slope intercept form of the equation.