How to find x and y limits of the equation matching a normalized fit function

How do you find the maximum x value, and max y value if you are interested in replotting and/or extending the max and min values for this:

x=[1 2 3 1 2 3 1 2 3]'
y=[1 1 1 2 2 2 3 3 3]'
z=[1 3 2 6 10 5 2 4 3]'
f=fit([x,y],z, 'poly22','Normalize','on')
figure
plot(f, [x,y],z)

I have never found a good way to do it. Thanks!

Note borrowing from: https://www.mathworks.com/matlabcentral/answers/346575-max-value-of-poynomial-surface-fit?s_tid=prof_contriblnk

[Astha Singh]

The statement does not make the query very clear. Are you looking for the maximum value of the surface plot? And what exactly is meant by 'extending the max and min values' here?

[KSSV]

YOu have it in hand already eh? The (x,y).