Maximum of a parameterized determinant

Let $f:\mathbb{R}\to\mathbb{R}$ be the function defined by $$f(x)=\det \begin{pmatrix} 1+x & 9 & 9 \ 9 & 1+x & 9 \ 9 & 9 & 1+x \end{pmatrix}.$$ Then the maximum value of $f$ on the interval $[9, 10]$ equals