Singular Values & the SVD · Hard problem

Let $A = \begin{pmatrix}4 & 0\\3 & -5\end{pmatrix}$. What fraction of $\|A\|_F^2$ (the total "energy") is captured by its best rank-one approximation $A_1$, i.e. find $\|A_1\|_F^2/\|A\|_F^2$?