The formula you need is Fz = F_max / R * (X-X_0)
F_max = max force at edge of circular plate (say 5000 N)
R = radius of circular plate (0.222 m)
X_0 = x distance from origin to center of circular plate (-0.222 m)
So, in this case, the formula would be Fz = 5000/0.222*(x+0.222)
Here is a link to a copy of your project with this formula.
Hope this helps.