[填空题]
$\text { Consider } f(x), g(x) \text { and } h(x)=(f \circ g)(x) \text {, for } x \in \mathbb{R} \text {. Given that } g(5)=8, g^{\prime}(5)=2 \text { and } f^{\prime}(8)=-4 \text {, find the gradient of the normal to the curve } y=h(x) \text { at } x=5 \text {. }$
