You say to yourself "Self ! This is easy, and I refuse to let it scare me !
I know that 20 dollars minus 2 dollars leaves 18 dollars.
And I know that 20 cows minus 2 cows leaves 18 cows.
And I know that 20 puppies minus 2 puppies leaves 18 puppies.
So it's obvious to me that 20 of anything minus 2 of the same thing
is always 18 of them.
It doesn't matter whether the things are hairbows, goldfish, cars,
CDs, books, or 'x', 'y', or 'z'.
So 20m minus 2m is definitely 18m."
