[填空题]
$\text { Given that }(x-4) \text { is a factor of } f(x)=x^{3}-2 x^{2}+a x+b \text { and that division of } f(x) \text { by }(x+2) \text { leaves a remainder of } 18 \text {, find the value of } a \text { and the value of } b \text {. }$a = b =
