MathNet 1984 — Part 01 Question 36

The positive reals $x$, $y$, $z$ satisfy $x^2 + x y + \dfrac{y^2}{3} = 25$, $\dfrac{y^2}{3} + z^2 = 9$, $z^2 + z x + x^2 = 16$. Find the value of $x y + 2 y z + 3 z x$.