While I was doing some remodeling work in the old brownstone I live in, I came across this treasure map. In order to unlock all the doors at the location of the treasure, I need to start at the starting point, and then travel in order from the first point to the fourth, gathering codes that will help me when I reach the final destination. Can you find equations of lines that will get me where I need to go?

Find the equation of a line that goes through the starting point to the point labelled first. Here is where I will find the first piece of the puzzle. What is it's slope, how do you know? What is it's y intercept? Put it in y=mx+b form.
Find the equation of the line that goes through the first point and the second point. I will find the second piece here. What is it's slope, how do you know? What is it's y intercept? Put it in y=mx+b form.
Find the equation of the line that goes through the second and third points. What is it's slope, how do you know? What is it's y intercept? Put it in y=mx+b form.
Find the equation of the line that goes through the third and fourth points. What is it's slope, how do you know? What is it's y intercept? Put it in y=mx+b form.
Finally, find the equation of the line that will take me to the treasure's location. What is it's slope, how do you know? What is it's y intercept? Put it in y=mx+b form.