Since you have 7 points, I expect that they will fit a polynomial of order 6 exactly.

So define your function as $\displaystyle \begin{align*} f(x) = a\,x^6 + b\,x^5 + c\,x^4 + d\,x^3 + e\,x^2 + f\,x + g \end{align*}$. When you substitute in each of the points, you will get 7 equations in 7 unknowns which can be solved simultaneously for a,b,c,d,e,f,g. I would advise using technology such as a CAS to do this