How to interpolate data points

I'm trying to answer the following question:

This is the code I have so far:

    function [f table] = interpol(x, xdata, ydata)
    N = length(xdata);
    A = zeros(N,N+1);
    A(:,1) = xdata;
    A(:,2) = ydata;

    for col = 3:N+1
            for row = 1:N-1 -(col-3)
                A(row,col) = (A(row+1,2+col-3)-A(row,2+col-3))/(A(row+1+col-3,1)-A(row,1));
            end
    end
    table = A(1:N-1,3:N+1);  
    f = ydata(end);
    for I = N:-1:1    
        f = f.*(x-xdata(I)) + A(1,I+1);
    end
end

This doesn't seem to be returning the right answers at the moment. Where do I go from here?

[Geoff Hayes]

Ollie - please add some comments to your code. What are the inputs? What algorithms have you implemented? Why do you think that incorrect answers are being returned?