chain rule

Let w = f (x, y), where x and y are functions of t. Then, according to the chain rule, dw/dt is equal to

Let $$\,\,W = f\left( {x,y} \right),\,\,$$ where $$x$$ and $$y$$ are functions of $$t.$$ Then, according to the chain rule, $${{dw} \over {dt}}$$ is equal to