13-7=
□+□=□ □-□=□□+□=□ □-□=□
[ ]
( )+( )=( )( )- 4 =( )
( )-( )=5( )+( )=12( )+( )=16( )-( )=4
□○□=□ □○□=□□○□=□ □○□=□