Find derivative of h(x)
[tex]\\ \sf\longmapsto \dfrac{d}{dx}(3x^2-4)[/tex]
[tex]\\ \sf\longmapsto 6x[/tex]
Now
x=-3
[tex]\\ \sf\longmapsto h(-3)[/tex]
[tex]\\ \sf\longmapsto 6(-3)=-18[/tex]