Question 1158869
Hi there,
The equation of a line is y = mx + c
m = gradient or slope
c = the line's y intercept 

Knowing the line's y intercept allows, with the x intercept, to work out the gradient or slope.
e.g. y = 4x + 8
To find where the line cuts the x axis make y = 0 
0 = 4x + 8
4x = -8
x = -2     Cuts x axis at (-2, 0)
To find where line cuts the y axis make x = 0
y = 4x + 8
y = 4(0) + 8
y = 8   cuts y axis at (0, 8)
To find the gradient use y2 - y1/x2 - x1
Using the example y = 4x + 8, the y intercept (0, 8) (x1, y1) and the x intercept (-2, 0)  (x2, y2)
y2 - y1/x2 - x1  = 0 - 8/-2 - 0  = -8/-2 = 4 The gradient (slope) in y = 4x + 8
Hope this helps, mate. :-)