add/sub

.model small
.stack 100h
.data
a db 10,13, "enter first value: $"
b db 10,13, "enter second value: $"
r db 10,13, "sum of three value : $"

    x db ?
    y db ?
.code


main proc
     mov ax,@data
     mov ds,ax

     lea dx,a
     mov ah,9
     int 21h

     mov ah,1
     int 21h

     mov x,al
     mov bl,x

     lea dx,b
     mov ah,9
     int 21h

     mov ah,1
     int 21h

     mov y,al
     mov cl,y

     lea dx,r
     mov ah,9
     int 21h

     add bl,cl
     sub bl,48

     mov dl,bl

     mov ah,2
     int 21h

     mov ah,4ch
     int 21h
     main endp
end main