Or you could even just build it up from basics, which is how I would expect it to be done. It's clear that 220 is the same as 120+120, then you can show that 32

Or you could even just build it up from basics, which is how I would expect it to be done. It's clear that 220 is the same as 120+120, then you can show that 320 = 220+120, etc etc. If they learn it that way at first, it should be clear to them that (60+2)(20) = 6020+220.