Find the critical points of the function

h(x)=3x4+8x348x2+3\displaystyle {h}{\left({x}\right)}={3}{x}^{{4}}+{8}{x}^{{3}}-{48}{x}^{{2}}+{3}

Enter your answers from smallest to highest.

smallest, at x=\displaystyle {x}=

middle, at x=\displaystyle {x}=

largest, at x=\displaystyle {x}=