(640-240):8+28:7=400:8+4=50+4=54
640-(240:8+28:7)=640-(30+4)=640-34=606
(640-240:8)+28:7=(640-30)+4=610+4=614
(640-240):8+28:7=400:8+4=50+4=54
640-(240:8+28:7)=640-(30+4)=640-34=606
(640-240:8)+28:7=(640-30)+4=610+4=614