how to sub 2 numbers in assembly code example

Example: subtract two numbers in assembly language

data segment
a dw 9A88h
b dw 8765h
c dw ?
data ends
 
code segment
assume cs:code,ds:data
start:
mov ax,data
mov ds,ax
mov ax,a
mov bx,b
sub ax,bx
mov c,ax
int 3
code ends
end start