Answer:
I'm gonna go a little out of order.
To determine b, find where the line crosses the y-axis. If it's positive, put it as " + " and if it's negative, put it as " - ".
To determine m, find two points on the line that are directly on the number. Example, choose (4, 1) instead of (4.1, 5.2). Go up/down and left/right (while making sure to count) until you reach the second number. going up and right will be considered positive while down and left are considered negative.
Using rise/run, put your number for up/down as a numerator over your left/right, which will be a denominator.
Insert m and b and you're good to go!