Subconvexity bound for $\mathrm{GL(3)} \times \mathrm{GL(2)}$ $L$-functions in $\mathrm{GL(2)}$ spectral aspect

Let $\pi$ be a Hecke-Maass cusp form for $\mathrm{SL(3, \mathbb{Z})}$ and $f$ be a holomorphic cusp form for $\mathrm{SL(2,\mathbb{Z})}$ of weight $k$ or a Hecke-Maass cusp form corresponding to the Laplacian eigenvalue $1/4+k^2$, $k\geq 1$, for $\mathrm{SL(2,\mathbb{Z})}$. In this paper, we prove the following subconvexity bound \begin{align*} L\left({1}/{2},\ \pi \times f\right) \ll_{\pi,\,\epsilon} k^{\frac{3}{2}-\frac{1}{51}+\epsilon}. \end{align*}