y = mx + c
Where m is the gradient and c is the y-intercept.
1) Slope of line
This is the gradient, which is verticle change divided by horizontal change, which if you use your A and B co-ordinates comes to 2.5x. This is what you got, which was 25/10x, but just simplified.
2) Intercept and Equation of line
Finding the intercept will basicly find the equation of the line. We know so far that y = 2.5x + c, as the gradient is m, which is 2.5. We then sub in the x and y values for either A or B. If we use A,
-3 = 2.5(0) + c
Therefore c = -3
This means we can sub -3 into c to get the equation of the line.
y = 2.5x -3
4) Scetching the line
This part is quite simple. Just draw a line that goes through points A (0,-3) and B (-10,-28). You can also mark on the line the y intercept, which should be - 3.