Yeah, this is some method of turning the 9 into 10, because it’s easier to add 10 and 7 than it is 9 and 8, but I don’t have enough info to help, because I just get told I’m doing it wrong by my kid. I was never into it either as a kid, but mental math would end up failing me later in life, so I’d like to help her, I just need more info!