y=mx+b is the equation we must fill out, with x and y being their respective coordinates, m being the slope, and b being the y-intercept. The y intercept will be at (0, y), and the beginning of this problem already gives us the y-intercept: -4.
We now know y=mx-4. To find the slope, m, we’ll plug in one of the coordinates: (5, 1). The new equation is 1=m(5)-4. Solve this to get 5=m(5), and then m=1.
Now that we know the slope and y-intercept, we can conclude that the equation is y=x-4.