How do you find the y-axis intercept of a straight line?

Using the equation of a straight line: y = mx + c (c is the y axis intercept, m is the gradient and y and x are points on the line (x,y))

e.g. if the gradient of the line was 3 and the line passes through the point (4,5) the equation would look like:

5 = 3(4) + c

5 = 12 + c

Rearrange:

c = -7 and therefore the line intercepts the y axis at (0,-7)