One way to do it without math. Cut a templet out of the left or right half tail plane. Use heavy paper or cardboard. Then put 3 small holes on the perimeter at different locations. Then suspend it on something with a pin. Make sure it hangs free. Draw a vertical plumb line from each of the three holes . Where the lines intersect draw a line parallel to the fuse. The MAC will be on that line 25% back from the leading edge.