largely a substitution exercise
involving trial and perseverance, with some thought maybe
"I'm thinking of a number and you don't know what it is (or do you...?)
here it is [write b]
whatever it is, I'll multiply it by 2 [put a 2 in front of the b]
then I'll add 5 to that
then I'll divide all this by 3 [maybe emphasise by drawing the line slowly, making sure that students are looking at the board]
what does this expression say happened to my number?
OK, all of this here [putting a hand over the expression] is 9
so what was my number?
good, now I'm interested in what other positive whole numbers that this expression could be..."
find a general form for the letters
possibly explaining why these work
what happens for the last one?