9.9×9+9.9=9.9×(9+1)=9.9×10=99
9.9×9+9.9=9.9×(9+1)=99
9.9×9+9.9=9.9×9+9.9×1=9.9×(9+1)=9.9×10=99
9.9x9+9.9=9.9x(9+1)=9.9x10=99