This uses £1 (100’s), 10pences (10’s) and pennies (units) to show what is being done when exchanging. I called it subtraction by borrowing as that’s what most teachers and pupils say. I prefer exchanging, as this is what is actually being done. Borrowing comes from the other method taught in the past, where the borrowed one is paid back. See a similar resource for division @ https://www.tes.com/teaching-resource/short-division-bus-stop-12297338