Question: finding cube of a number

[Visual Basic.Net]

I wrote this to multiply the x by itself 3times then add a number y to it and save result in z. but it dosn't giving me the right result.

.DATA
X DB 12h
Y DB 34h
Z DW ?,?

mov al,x
mov bl,x
mul bl; ax=bl*al
mul ax; dxax=ax*ax
add ax,y
mov z,ax
mov z+2,bx

I wrote it in Debug.
thank's