There are thousands of answers to these questions but I would give the most simple answers.
7. Lets say points (-1,-1), (0,0), (1,1)
8. y = x
Explanation: The y-intercept would be 0. In order from (0,0) to go to (1,1), we need to go up one unit and right 1 unit so, by rise/run, the slope would be 1/1 or simply 1. by plugging into the equation y = m(slope)x + b(y-intercept).
(Desmos is a great website)