Let's split this problem into several steps:
Let's first put it into the point-slope form:
⇒ Point-slope form ⇒

- (x0,y0) --> any point on the line
- m --> slope
Consider the information given:
- (x0,y0) --> (-4,15)
- m --> -4
Let's plug the numbers in:

To put this format into slope-intercept form, we will solve for y:
⇒as in, move everything else to one side and y by itself on the other

Thus the equation of the line is -->

Hope that helps!