Thanks to everyone who helped me with the previous questions
Last question:

Answer:
y=-3x+7
Step-by-step explanation:
Rise/run
To find slope you can use the rise/run strategy. You count how many units up/down and then how many right/left. between each point on the line, it was down 3 units, right 1 unit (3/1) and since it was going down it would be negative.
As for the y-intercept, you look at where the line crosses the y-axis. In this case it was at (0,7), so the answer would be 7.
Plug your answers in and your equation should be y=-3+7.
You could also do y=7-3x, its the same equation but reversed, so you'll get the same line.
Hope this helps :)