DATA SEGMENT
        A DD 30H
        B DD 50H
        RES DD ?
DATA ENDS

CODE SEGMENT
ASSUME  DS:DATA, CS:CODE
START:
        MOV AX,DATA
        MOV DS,AX

        MOV AX,DS:WORD PTR A
        ADC AX,DS:WORD PTR B
        MOV BX,DS:WORD PTR A+2
        ADD BX,DS:WORD PTR [B+2]
        MOV DS:WORD PTR RES,AX
        MOV DS:WORD PTR [RES+2],BX

        MOV AX,4CH
        INT 21H

CODE ENDS
END START

OUTPUT
***********

 ax 0080