68*99+99 =99*69=(100-1)*69=6900-69=6831
68*99+99=(68+1)*99=67*99=69*(100-1)=69*100-69=6900-69=6831
68*99+99=68*99+1*99=(68+1)*99=69*99=69*(100-1)=6900-69=6831
