Can anyone figure out my grandson's Year 4 Math homework? (He is 8!)

I've attached a photo of it.

The Easy and Speedy part is fine.

However "Some subtracting" is weird - those middle numbers crossed out are on the original sheet. I can't figure out how they work. The subtractions themselves obviously work if you just ignore the crossed out numbers, and adjust for hundreds, tens and units, but why are the crossed out numbers there in the first place? They must be some sort of working out, but what? I come up with a rule that explains some of them but I can't explain them all.

Then finally there is 12, 13 and 14: "Choose three numbers to create a 3-digit number. Re-arrange the digits and subtract the smaller number from the larger number. Do this three times". This doesn't seem to me very clear. Is this what they are looking for:

Choose three numbers: 1 8 6

Re-arrange the digits and subtract the smaller number from the larger number: 8 - 6 - 1 = 1

Do this three times - just choose three numbers another two times?

Choose three numbers: 3 9 2

rearrange and subtract: 9 - 3 - 2 = 4

Choose three numbers: 3 8 2

rearrange and subtract: 8 - 3 - 2 = 3

But since these follow from 9, 10 and 11 perhaps the three numbers are similar to those? But I don't see how?

Anyway here are the original questions: