A good place to start when you want to learn how to find a midpoint of a line is a circle. Take the diameter of a circle, for instance if the coordinates of the starting point are (1,6) and the coordinates for the ending point are (11,6). The midpoint of a line is the exact central point where a line through these two points would meet. Now the value of y is a constant one as the line runs parallel to the x-axis, the value of x changes by 10, the half of which is 5, this is not the midpoint though because if you remember the line started at x=1 so 1+5 is 6, so the midpoint coordinates are (6,6). This is how you get the midpoint of a line.