Suppose $x, y, z \in \mathbb{R}^+$, such that \begin{align*} x^2 + y^2 + xy &= 9\\ y^2 + z^2 + yz &= 16\\ z^2 + x^2 + zx &= 25 \end{align*} Find the value of $xy+yz+zx$.