Making sure variable is an integer?

If I did it right, I get 215 tables and 136 chairs:

       --A--- -B-- -C-- -D-- ---E--- -F- -------------G-------------- --H-- ----I-----
  13   Profit wood prod time Fitting box           Formula            Value Constraint
  14   tables 215   70   20    72     1              =20*x + 12.5 * y  6000 <= 6000   
  15   chairs 136   30  12.5   18     1                        =x + y   351 <= 400    
  16          > 0  > 0                               =72 * x + 18 * y 17928 <= 18000  
  17                                     =SUMPRODUCT(B14:B15,D14:D15)  6000 maximize