Explanation:
grab two points from the line then subtract x with x and y with y and you will get a fraction which will be mx and -7 will be your b
y=(the answer you got)*mx*-7
this is how you sub then
1-1
2-3 and it will look like a fraction
i explained it better for you but you have to do the work so you can better understand it
(you can always find b by looking for the point on the y-axis the line crosses)