>>282214166
For multiples of 9, Just move one number after 9 to left for each iteraction.
In case of 9*8, you move 7 digits from 9 to left and what rests is 9-7, which is 2, getting 72. If it's still too confusing, decorate that 9*9 is 81 and set it as a basis for other maths and do the contrary, as in moving 1 from 8 to right.
I wonder if periodic decimal would make Rinrin excited though.

i want to eat rinrin's coord