Singular Values & the SVD · Hard problem

Every square matrix has a polar decomposition $A = QS$ with $Q$ orthogonal and $S = \sqrt{A^{T}A}$ symmetric positive semidefinite; from the SVD, $S = V\Sigma V^{T}$. For $A = \begin{pmatrix}3 & 0\\4 & 5\end{pmatrix}$, find the entry of $S$ in row 1, column 2. Give your answer in simplest radical form.